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The growth and flowering of Hymenocallis × festalis
Scientia Horticulturae, 30 (1987) 301-313
301
Elsevier Science Publishers B.V., Amsterdam - - Printed in The Netherlands
The Growth and F l o w e r i n g of HymenocalUs X festaUs GORDON R. HANKS 1 and STEPHEN K. JONES
Glasshouse Crops Research Institute, Littlehampton, West Sussex BN17 6LP ( Gt. Britain) (Accepted for publication 27 June 1986)
ABSTRACT Hanks, G.R. and Jones, S.K., 1987. The growth and flowering of HymenocaUis xfestalis. Scientia Hortic., 30: 301-313. Bulbs of Hymenocallis (including Ismene) have showy, fragrant flowers. Little is known of the horticultural potential of these plants, and observations and trials on a stock of Hymenocallis X festalis are described. In a stock of glasshouse-raised bulbs, bulb grade exerted a marked effect of the number of florets produced, which increased from 2 in 9-10-cm-circumference bulbs, to 7 in 18-19-cm-grade bulbs. Field-raised bulbs of the same grades produced fewer florets. Bulbs were usually planted for flower production in the glasshouse in April; earlier planting (February) leading to greater floret size but a longer period in the glasshouse before anthesis. Planting could be delayed at least until June, or later flowering could be achieved by storing the dry bulbs over winter at a low temperature (5 ° C ), but the latter treatment reduced the percentage of bulbs which flowered. The long scapes could be dwarfed by ethephon (as Ethrel). Hot-water treatment, as a pest and disease control measure, did not result in damage to the flowers provided it was delayed until after the staminal cup initial had been formed. In the field, growth of the main bulb was more vigorous than in the glasshouse, but pot culture in the glasshouse led to copious offset production. Data are presented for bulb increases for various grades of bulbs planted in outdoor beds at rates of 350-1050 g per metre row. Keywords: bulb production; flowering; Hymenocallis; Ismene. Abbreviations: H.W.T. = hot-water treatment; I.S.D. = internal stage of floral development.
INTRODUCTION
The genus HymenocaUis (Amaryllidaceae), including Ismene, comprises some 35 species distributed over the southern U.S.A. and South America ~Present address: M.A.F.F., Kirton Experimental Horticulture Station, Kirton, Boston, Lines. PE20 IEJ, Gt. Britain.
0304-4238/87/$03.50
© 1987 Elsevier Science Publishers B.V.
302
( Synge, 1969). The bulbs are cultivated for their fragrant white or, in H. amancaes and H. × spofforthiae, yellow flowers. Species noted in commerce include H. amancaes, H. harrisiana, H. littoralis and H. speciosa, along with the following hybrids ofH. narcissiflora: Hx[estalis, together with the selection Zwanenburg (hybrid with H. longipetala); H. X macrostephana forms 'Daphne' and 'Advance' (with H. speciosa); H. 'Sulphur Queen' (H. ×spofforthiae) (with H. amancaes ). The sub-genus Ismene ( H. amancaes, H. narcissiflora and H. pedunculata) is characterized by a staminal cup longer than the inflexed filaments. The sub-genus Hymenocallis has the staminal cup shorter than or subequal to the erect spreading filaments (Synge, 1969). Traub (1962, 1963) recognised four s u b - g e n e r a - HymenocaUis (s.s.), Elisena, Pseudostenomesson and Ismene m but he and other students of the group (e.g. Flory, 1976) retained HymenocaUis as the generic name, and Ismene was included under HymenocaUis by K.A.V.B. (1963). On the other hand, Sealy (1954) restricted his monograph to Hymenocallis s.s.. On the basis of cultural requirements and geographical distribution, the designation Ismene seems useful; plants in this group may be grown (in the U.K. ) outdoors in a sheltered position, and occur, along with Elisena and Pseudostenomesson, in South America, rather than in North America and the West Indies as does Hymenocallis s.s.. The Old-World genus Pancratium is distinguishable from HymenocaUis by the many ovules in each loculus. The large dry dormant bulbs of Hymenocallis are sold in winter and spring either for forcing into bloom in April-May or, in the case of the Ismene subgenus, for growing in a sheltered outdoor position. Species of HymenocaUis s.s. are regarded either as evergreen stove plants (e.g.H. speciosa) or deciduous glasshouse plants (e.g.H. harrisiana) (Synge, 1969). Hymenocallis is a very minor component of the bulb trade, with some 24 000 bulbs imported to The Netherlands in 1980-1981 (Anon., 1982), but the showy, fragrant inflorescences coupled with the vigorous growth of the hardier species hint at the potential value of the genus (Fig. 1 ). Observations of a small stock of H. ×[estalis, maintained at the Glasshouse Crops Research Institute (G.C.R.I.) for a number of years, contributed to this impression, and prompted the trials described in the present paper. The effects of bulb grade, storage temperature and duration, growing conditions, growth retardants and hot-water treatment on flowering performance, and of bulb grade, cultural conditions and planting rate on bulb yields were examined. MATERIALS AND METHODS
Stock bulbs of Hymenocallis Xfestalis (Worsley) hort. were grown individually in 19-cm-diameter pots of G.C.R.I. 2:1 mix (peat/sand compost (3:1 v/v) and John Innes No. 2 compost, 2:1, v/v) in a glasshouse at a minimum maintained temperature of 16°C and ventilated at 18°C. From 1979, stocks were
303
(a)
(b) Fig. 1. The growing plant (a) and a single flower (b) of Hymenocallis×festalis. Photograph G.C.R.I.
304 also grown in ridges in the field at Littlehampton, on soil of the brickearth type. Stocks were planted in April, and dried off in pots or lifted from the field in October. After cleaning and cutting off leaves (but leaving the root systems undamaged), bulbs were dipped at ambient temperatures for 3 h in 0.05% a.i. lindane (as Lindex Miscible 10% ) with 0.1% wetter (PBI Spreader) followed by 30 rain in 0.2% a.i. benomyl (as Benlate 50% W.P. ) with 0.5% a.i. captafol (as Sanspor 50% ) and 0.1% wetter to control bulb fly and red spot disease (Stagonospora curtisii), respectively. Bulbs were then dried and stored at ca. 17°C. Details of individual experiments are given under Results. H.W.T., used to control a variety of bulb pests including bulb fly, and combined with a fungicidal treatment, consisted of a 3-h dip at 44 °C in 0.2% a.i. benomyl (as Benlate 50% W.P.) and 1.0% a.i. dithiocarbamate (as Maneb 80% W.P.). Growth retardants were diluted from stock solutions of ancymidol (Lilly Research Centre), ethephon (as "Ethrel-E", 2-chloroethylphosphonic acid) ( I.C.I. Plant Protection Division) and chlormequat chloride (as "3C Cycocel" ) (Applied Horticulture). In assessing flowering performance, the following records were routinely made: glasshouse period (days in the glasshouse until opening of the first floret), scape length (bulb tip to base of pedicel), first floret size (maximum diameter of the staminal cup), and floret number. For the growth-regulator experiment, stem length was measured when treatments were applied, and used as a co-variate to adjust subsequent data. Where S.E.D.'s are quoted for experiments with variable replication, these are the values for comparisons between a treatment having the minimum number of replicates and one with the maximum number. RESULTS
Aspects of flowering performance Bulb grade, m Glasshouse-raised bulbs, grades 9-10 up to 18-19 cm circumference, were stored at ca. 17°C from lifting until planting and transfer to the glasshouse on 15 April 1981. Flowering performance is shown in Table I. Only 25% of bulbs in the smallest grade (9-10 cm) produced flowers, but at least 90% did so in bulbs larger than 13 cm. Glasshouse period was slightly longer in the larger grades (43 days in the smaller grades, 49 days in the largest). Scape length increased steadily with increasing bulb size, from 371 to 545 ram. There were no significant effects of bulb grade on floret size, but floret number increased with bulb size, from about 2 in the smaller grades to 7 in the largest. To obtain an average of 4 florets, a bulb of at least 13 cm circumenference was needed. The mean number of emerged leaves per plant at anthesis was 7-8.
305 TABLE I Flowering performance of 10 grades of glasshouse-grown bulbs of replicates of each grade (15 for 18-19 cm)
HymenocaUis. Figures
are means for 20
Bulb grade (cm circumference)
Plants reaching anthesis (%)
Glasshouse period (days)
Stem length (ram)
First floret size (ram)
Floret number
Leaf number
9-10 10-11 11 - 12 12-13 13-14 14-15 15-16 16-17 17-18 18-19
25 70 80 80 90 100 95 95 100 100
43.3 43.1 43.4 42.2 43.7 42.7 44.8 44.7 49.2 48.9
371 368 403 407 424 430 451 501 518 545
31.5 30.4 30.3 31.1 31.4 30.4 30.8 31.1 31.5 31.8
2.3 2.1 2.9 3.4 4.0 4.7 5.6 5.5 6.3 7.2
6.8 6.8 7.4 7.2 7.3 7.3 8.0 7.5 7.6 7.5
0.52
0.35
S.E.D.
2.14
26.4
1.09
Temperature of bulb storage. ~ Field-raised bulbs of grades 12-14, 14-16 and
16-18 cm circumference were stored at 5, 17 or 20 °C from lifting until planting and transfer to the glasshouse on 21 April 1982. Flowering performance is shown in Table II. In contrast to the glasshouse-grown bulbs of the previous experiment, a lower percentage of bulbs flowered, and these had smaller numbers of florets. Overall, 35% of bulbs reached anthesis following 5 ° C-storage, and about 70% following 17 or 20 ° C-storage, the remainder of the plants remaining vegTABLE II Flowering performance of 3 grades of bulbs of Hymenocallisfollowing storage at different temperatures. Date based on 20 replicate bulbs for each treatment combination
Bulb grade (cm circum-
Storage temperature
Plants reaching
Glasshouse period
Stem length
First floret
ference)
( °C )
anthesis ( % )
(days)
(ram)
size ( m m )
12-14
5 17 20
15 65 90
109.5 36.9 28.7
810 347 331
35.5 32.2 32.0
2.5 2.4 2.2
14-16
5 17 20
50 90 75
108.6 37.1 29.4
765 349 340
32.0 31.9 32.4
2.4 2.7 2.7
16-18
5 17 20
40 60 45
103.6 38.4 30.2
753 374 355
29.0 31.8 32.2
2.4 4.0 4.0
S.E.D.
2.69
34.5
1.23
Floret number
0.55
3O6 TABLE III Flowering performance of field-grown 14-16-cm Hyrnenocallis bulbs following storage for various durations at 17 ° C. Data based on 20 replicate bulbs for each treatment combination Date of end of storage
Plants reaching anthesis ( % )
Glasshouse period
Stem length (ram)
First floret size (mm)
Floret number
378 349 349
35.1 31.9 29.7
2.5 2.7 2.8
(days) 23 February 21April 15 June S.E.D.
85 90 90
71.4 37.1 22.5 1.55
13.9
0.60
0.25
etative. Floret number reached 4 in the largest grade of bulbs (16-18 cm) following storage at 17 or 20°C, and was ca. 2.5 in other cases. Glasshouse period and stem length decreased with increasing storage temperature, with no effect of bulb grade or interaction between the factors. After 5 ° C-storage, glasshouse period was very prolonged and stems very long (107 days and 767 m m overall), compared with values of 29 days and 339 m m for bulbs stored at 20 ° C. First floret size showed no effect of bulb size following 17 or 20 ° storage, although it fell with increasing bulb size after 5 ° C-storage. Duration of bulb storage. ~ Field-raised bulbs, grade 14-16 cm, were stored at 17°C until planting and transfer to the glasshouse on 23 February, 21 April and 15 June 1982. The results are shown in Table III. The percentage of bulbs reaching anthesis, and the number of florets, were in conformity with the results of the previous experiment, and were unaffected by storage duration. Glasshouse period, stem length and first floret size all fell following longer storage; there was a marked effect of delaying planting from February to April, and a smaller effect of a further delay until June. Performance of glasshouse- and field-raised bulbs. - - Bulbs of grade 14-16 cm, raised in the glasshouse, were re-planted in April 1983 either in the glasshouse or in ridges in the field. They were lifted in October, stored at 17 ° C until April 1984, and then both batches were grown in the glasshouse. Flowering performance was assessed in each year, and is shown in Table IV. Bulbs grown initially in the field or glasshosue had equal floret sizes and numbers, but anthesis was earlier and stems longer in the glasshouse. In the next year, when both lots were grown in the glasshouse, the ex-field bulbs flowered earlier and with shorter stems, but bore larger and distinctly more florets (see also the section on bulb growth under glass and in the field, below). Effects of growth retardants, m Field-raised bulbs, grade 16-18 cm, were planted in the glasshouse in April 1982. On 2 June (average stem length 103 ram), 300
307 TABLE IV Flowering performance of glasshouse-raised bulbs of HymenocaUis (A) in the field or glasshouse in 1983, and (B) of these bulbs grown in the glasshouse in 1984. Means based on 30 plants each Cultural conditions
(A) Ex-glasshouse Field Glasshouse S.E.D. (B) Glasshouse Ex-field Ex-glasshouse S.E.D.
Plants reaching anthesis ( % )
Time to anthesis (days)
Stem length (ram)
First floret size (ram)
Floret number
97 100
39.6 16.5 0.98
400 544 10.5
30.0 30.4 0.40
5.1 4.9 0.24
97 90
21.5 35.9 0.82
539 576 16.2
32.0 30.0 0.42
5.8 3.7 0.30
ml per pot compost drenches were given, and further watering was subsequently restricted for 3 days, the plant pots being placed on "saucers" for the whole of this period. The treatments consisted of ancymidol (1.25, 2.5 or 5.0 mg a.i. per pot), ethephon (960 or 1920 mg a.i. per pot) and chlormequat chloride ( CCC ) ( 2500 or 5000 mg a.i. per pot); controls received plain water. Ethephon delayed anthesis by 3-6 days compared with controls; ancymidol and chlormequat had no effect ( Table V). Ancymidol and chlormequat ( at all concentrations tested) reduced stem length by ca. 10% while ethephon at 960 TABLEV Effect of growth r e t a r d a n t t r e a t m e n t s on flowering performance of HyrnenocaUis bulbs. Five replicate bulbs per t r e a t m e n t , data are m e a n s of t h e indicated n u m b e r of bulbs reaching a n t h e s i s
Treatment (raga.i.per pot)
Number of plants reaching anthesis
Glasshouse period (days)
Stem length (mm)
Control
5
51.5
490
Ancymidol 1.25 2.50 5.00
4 5 5
52.8 51.3 51.1
451 454 453
E t h e p h o n 960 1920
5 5
57.2 54.5
385 250
Chlormequat 2500 5000
4 5
51.5 52.4
455 442
S.E.D.
1.24
28.3
308 and 1920 mg a.i. per pot reduced length by 21 and 49%, respectively. There were no significant effects of retardants on first floret size or floret number, which averaged 31.0 m m and 3.8, respectively, and no adverse effects of retardants on flower or plant quality were seen.
Effect of date ofH. W. T. m Field-raised, 17 oC-stored 10-12-cm bulbs were subjected to H.W.T. and bulb dissection to determine I.S.D. at monthly intervals from 2 November 1982 to 21 March 1983. A further batch of bulbs remained untreated. All treated bulbs were planted and transferred to the glasshouse on 19 April 1983. Bulb I.S.D.'s at treatment, and the subsequent flowering performance of the treated bulbs (including an assessment of H.W.T. damage to the florets), are given in Table VI: Except when the treatment was given at the last date, when perianth and androecium initials were already well formed, H.W.T. resulted in fewer plants reaching anthesis, in damaged, small florets, and lower floret numbers. There were no clear effects on anthesis date. Floret damage, which was extensive following H.W.T. between 7 December and 14 February, took the form of deformation of the perianth accompanied by, at later dates, damage to the androecium. Earliest H.W.T. (2 November) resulted in little floral damage in those plants reaching anthesis, although this number was reduced to 65%. H.W.T. at the latest date (21 March) resulted in no obvious damage; flowering performance being similar to that of the untreated controls. Aspects of bulb yields Bulb growth under glass and in the field, m Glasshouse-raised bulbs, grade 14-16 cm, were stored at 17°C after lifting and then planted in April 1983 either in the glasshouse or in ridges in the field (30 bulbs each). After one season's growth, mean whole bulb weights (including main bulb and offsets) were similar in either case (227 and 230 g). However, although the mean grades of the main (central) bulb were also similar (16-17 cm circumference), a greater proportion of the total weight of the glasshouse-grown bulbs was due to offset production. In a further trial, field-raised bulbs of grades 10-12 and 12-14 cm were stored over winter at 17 ° C and planted in April 1983 either in the 16 °C glasshouse or in a cold glasshouse ( m i n i m u m maintained temperature 5 ° C, ventilated at 10 ° C). To simulate different durations of growing season, leaves were removed and bulbs lifted and dried on 4 dates (30 August, 13 September, 27 September or 11 October). Bulb grade (main bulb) and bulb weights (main bulb and offsets) were then determined. Prolonging the growing season enhanced the growth of the main bulb and offsets, and growth was somewhat better in the cool glasshouse than in the warm glasshouse (Fig. 2 ). The analysis of variance indicated that there were no interactions between planted bulb grade, glasshouse temperature and length of growing season, hence the marginal or overall
Sp P A
G G or C (C) 3
2 Nov. 7 Dec. 10 Jan.
14 Feb. 21 Mar. None
75 95 95
65 50 45
Plants reaching anthesis ( %)
1.21
51.5 50.7 52.8
51.7 48.4 53.2
Glasshouse period (days)
28.4
433 458 424
417 268 281
Stem length (ram)
2.26
28.3 30.9 30.7
31.2 27.5 26.0
First floret size 2 (ram)
0.29
2.1 2.9 2.7
2.3 1.6 2.2
Floret number
87 0 0
15 100 100
(%)
Flowering plants with damaged florets
Split stamina] cup Perianth deformed in all florets Perianth deformed in all florets; some anthers deformed Ditto None None
Floral damage
1Sp = spathe initial visible; P = perianth segment initials visible; A = androecium initials visible; G = gynoecium initials visible; C = staminal cup initials visible. 2For 7 Dec. to 14 Feb. treatments, floret sizes based on reduced number of replicates because of extensive floret deformity. 3Determined at planting.
S.E.D.
I.S.D. of first floret at H.W.T.~
Date of H.W.T. (1982/83)
Effects of H.W.T. of Hymenocallisat various stages of floral development on floret damage and other aspects of flowering performance. Means for flowering performance based on 20 bulbs each. I.S.D.'s based on 10 bulbs each
TABLE VI
310
18f
16
i
L~
ill
Z
200 W h o l e bulb
I
180
IMainbu,b
o) 160
T
J~ J~
I
Z
140
E
.?.
i
.m
.2
#
T
IO0
i 8O
Bulb g r a d e
(cm)
Glasshouse temp. ( ° C )
D a t e of d r y i n g - o f f bulbs
Fig. 2. Effect of bulb grade (cm circumference) at planting, glasshouse temperature (minimum ° C/ventilation ° C) and date of drying-off bulbs on weight of main bulb and whole bulb cluster, and grade of main bulb of harvest. Data are marginal means for the three factors, based on 10 replicate bulbs for each treatment combination. Vertical bars are S.E.D.'s.
means for the three factors are shown. In the best conditions (cool glasshouse, grown until October) a 10-12-cm bulb yielded a 17-cm-circumference bulb weighing 121 g and a 12-14-cm bulb yielded an 18-cm bulb weighing 147 g; comparable values for warm glasshouse bulbs were 17 cm, 116 g (for a 10-12cm bulb planted) and 19 cm, 149 g ( for a 12-14 cm bulb planted). Glasshousegrown bulbs produced numerous offsets. Bulb planting grade and planting rate. ~ Field-raised bulbs of grades 6-8, 8-10, 10-12 and 12-14 cm circumference were planted outside in a bed in April, in weighed, counted lots, in 1-m rows 30 cm apart, at planting rates corresponding to 350, 700 and 1050 g of bulbs m - 1. Each grade-rate combination was duplicated in two plots, being randomly allocated within plots, and with guard plants at the extremities of the plots. The trial was repeated in two growing seasons (1981 and 1982). In September, bulbs were graded and the number and weight
311
1981
1.5
Grade (cm) planted - - o - - 6-8 ---A---•- - ' 0 " - - "
---V---
--
o
1982 ~
8-10 10-12
--
A ,.~ .~
12-14
¢u c
o
.¢: .2
1.0
o --'.'-.~ .-~.... o.__
I
--v
. . . .
=-----.~.---v I
5 o
0.5
I
35O
I
I
I
700
1050
350
1 700
I 1050
Plantingrate ( g / m ) Fig. 3. Bulb yields (expressed as log, of final weight divided by planted weight ) in Hymenocallis bulbs of 4 grades grown at 3 planting rates (weight of bulb per metre run) in two seasons. Values are means of duplicate plots for each year. Vertical bars are S.E.D.'s.
of bulbs in each grade were recorded. Bulb growth was greater in 1982 than in 1981, with a more marked decline in bulb growth with increased planting rate in the lateryear (Fig. 3 ). There was a significanteffectof planted bulb sizeon weight increase:in 1981 there was an overallincrease (across allplanting rates) of 220% for 12-14-cm bulbs, increasing to 290% for 6-8-cm bulbs, with corresponding figures of 265 and 330% for 1982. Only the larger grades of bulbs produced offsets.In 1982, for example, bulb numbers increased by 140% in the 12-14-cm planted grade, with no effectof planting rate. DISCUSSION
Our observations confirmed H. X[estaliz as a highly attractive and vigorous ornamental. There appears to be no detailed information on the horticultural performance of Hymenocallis available in the literature, so the findings summarised below should provide guidelines for potential growers of this crop. A major consideration is that individual florets are relatively short-lived, so that large bulbs are needed to obtain a satisfactory floret number to extend the flowering period. In a 16°C-glasshouse, successive florets open at 1-2 day intervals, each floret remaining in reasonable condition for 2-3 days. Floret number increased markedly in the larger bulb grades: in one trial with glasshouse-raised bulbs, floret number increased from 2 (for a 9-10-cm bulb) to 7 (18-19-cm bulb), but field-raised bulbs of the same sizes produced fewer florets. Generally, bulbs greater than 13-cm-grade flowered reliably, but to ensure at least a reasonable floret number (4), a bulb of 16-18 cm should be used. Planting bulbs in the glasshouse relatively early (February) led to greater
312 flower size compared with bulbs planted in April-June, but the time in the glasshouse to anthesis was prolonged. Later anthesis could be achieved by delaying planting until June (anthesis in 3 weeks), or by storing bulbs over winter at a low temperature. However, the latter also greatly reduced the percentage of bulbs which flowered. Flower quality of both glasshouse- and fieldgrown bulbs were similar, but stems were longer in the former. The stems of HymenocaUis, which are excessively tall for pot-plants, were successfully dwarfed by compost-drenching with ethephon, with no adverse effectson flower quality: ancymidol and chlormequat had only slight effects on stem length at the concentrations used. H.W.T., if required as a pest and disease control measure, did not damage florets if given shortly before planting, when the staminal cup initialwas visible upon bulb dissection. Bulb growth was more vigorous when plants were grown in the field than in the glasshouse, and it appeared that a long growing season is important in obtaining large bulbs capable of forming a satisfactory number of florets.Outdoors, the growing season was limited by the onset of frost, but an early light frost damaged only the foliage. In the glasshouse, but not in the field,copious offset bulbs were produced, perhaps because of higher temperatures around the bulb. In bulbs grown in beds, although bulb growth differed from year to year, weight increases of 200-300% were obtained. Lower planting rates (350 g m -I) were especially beneficial for the smaller grades of bulbs. Some practical problems were encountered in growing the Hymenocallis stock. The large, fleshy contractile roots cause difficultyin cleaning bulbs and in liftingfrom the field,when the basal plate of the bulb can easilybe damaged (deep planting should be avoided). Some problems were encountered with leaf scorch or red spot disease ( Stagonospora curtisii) and large bulb-fly (Merodon equestris), but these were controlled by the measures used. Vegetative propagation of H. ×[estalis should present few problems. Numerous offsets are produced by pot-grown plants cultured in the glasshouse, and it may also be propagated easily by the "twin-scaling" technique (G.R. Hanks, unpublished data, 1982 ). The large photosynthetic seeds of HymenocaUis have attracted some attention (Whitehead and Brown, 1940; Flint and Moreland, 1943 ). Under our conditions few seeds were set, but the seedlings were vigorous, producing flowering-size bulbs in about 3 years. The present G.C.R.I. stock of H. ×festalis was confirmed as such by reference to the descriptions given by Synge (1969) and by chromosome counts in Feulgens and aceto-carmine root-tip preparations (see Flory, 1976). In our stock, 2n=ca. 64; Flory (1976) gives H. ×festalis as 2n=62-64, with the parents H. narcissiflora (H. calathina ) and H. longipetala (Elisena longipetala ) with 2n= 104-110 and 50, respectively. Flory (1976) listed somatic chromosome numbers for over 100 accessions of Hymenocallis ranging from 38 to 110, with a further single accession having 2n= 195; he noted, in several taxa, differences in chromosome numbers between different accessions of the same
313 taxon. Several hybrids are known, and hybridization occurs freely, both within and between the sub-genera (e.g. see Raina and Khoshoo, 1971 ). This genetic diversity and ease of hybridisation make Hymenocallis breeding an attractive proposition, while the discovery of new species adds to these resources; for example, a new species H. heliantha ( sub-genus Ismene), with potential in its large yellow flowers and small plant size, has recently been described (Ravenna, 1980). Even with the present species and hybrids there is clear potential for the greater horticultural exploitation of Hymenocallis. A wider market for plants like H. ×festalis, sold as a large prepared bulb complete with pot and compost, like Hippeastrum, is suggested. ACKNOWLEDGEMENTS We thank Lilly Research Centre for a gift of ancymidol, A.A. Tompsett (Rosewarne Experimental Horticulture Station) for information on bulb dip and H.W.T. treatments, and F.A. Langton and R. Menhenett for valuable comments on the text.
REFERENCES Anonymous, 1982. Invoer bloembollen in Nederland. Bloembollencultuur, 93: 91. Flint, L.H. and Moreland, C.F., 1943. Note on photosynthetic activity in seeds of the spider lily. Am. J. Bot., 30: 315-317. Flory, W.S., 1976. Distribution, chromosome numbers and types of various species and taxa of Hymenocallis. Nucleus, 19: 204-227. K.A.V.B. (Koninklijke Algemeene Vereeniging voor Bloembollencultuur), 1963. Classified list and internationalregisterof hyacinths and other bulbous and tuberous rooted plants.K.A.V.B., Haarlem, 214 pp. Raina, S.N. and Khoshoo, T.N., 1971. Cytogenetics of the tropicalbulbous ornamentals. V. Chromosomal variation and evolution in Hymenocallis. Cellule,68: 239-259. Ravenna, P., 1980. A new yellow-floweredHymenocaUis (Amaryllidaceae) from North Peru. Bot. Not., 133: 97-98. Sealy, J.F., 1954. Review of the genus Hymenocallis. Kew Bull.,2: 201-240. Synge, P.M., 1969. Supplement to the Dictionary of Gardening. Clarendon Press, Oxford, pp.
358-360. Traub, H.P., 1962. Key to the subgenera,alliances and species of Hymenocallis. Plant Life, 18 (The AmaryllisYearBook): 55-72. Traub, H.P., 1963. Generaof Amaryllidaceae.The AmericanPlant Life Society,La Jolla, CA, 85 PP. Whitehead, M.R. and Brown, C.A., 1940. The seedof the spider lily, HymenocaUisoccidentalis. Am. J. Bot., 27: 199-203.
301
Elsevier Science Publishers B.V., Amsterdam - - Printed in The Netherlands
The Growth and F l o w e r i n g of HymenocalUs X festaUs GORDON R. HANKS 1 and STEPHEN K. JONES
Glasshouse Crops Research Institute, Littlehampton, West Sussex BN17 6LP ( Gt. Britain) (Accepted for publication 27 June 1986)
ABSTRACT Hanks, G.R. and Jones, S.K., 1987. The growth and flowering of HymenocaUis xfestalis. Scientia Hortic., 30: 301-313. Bulbs of Hymenocallis (including Ismene) have showy, fragrant flowers. Little is known of the horticultural potential of these plants, and observations and trials on a stock of Hymenocallis X festalis are described. In a stock of glasshouse-raised bulbs, bulb grade exerted a marked effect of the number of florets produced, which increased from 2 in 9-10-cm-circumference bulbs, to 7 in 18-19-cm-grade bulbs. Field-raised bulbs of the same grades produced fewer florets. Bulbs were usually planted for flower production in the glasshouse in April; earlier planting (February) leading to greater floret size but a longer period in the glasshouse before anthesis. Planting could be delayed at least until June, or later flowering could be achieved by storing the dry bulbs over winter at a low temperature (5 ° C ), but the latter treatment reduced the percentage of bulbs which flowered. The long scapes could be dwarfed by ethephon (as Ethrel). Hot-water treatment, as a pest and disease control measure, did not result in damage to the flowers provided it was delayed until after the staminal cup initial had been formed. In the field, growth of the main bulb was more vigorous than in the glasshouse, but pot culture in the glasshouse led to copious offset production. Data are presented for bulb increases for various grades of bulbs planted in outdoor beds at rates of 350-1050 g per metre row. Keywords: bulb production; flowering; Hymenocallis; Ismene. Abbreviations: H.W.T. = hot-water treatment; I.S.D. = internal stage of floral development.
INTRODUCTION
The genus HymenocaUis (Amaryllidaceae), including Ismene, comprises some 35 species distributed over the southern U.S.A. and South America ~Present address: M.A.F.F., Kirton Experimental Horticulture Station, Kirton, Boston, Lines. PE20 IEJ, Gt. Britain.
0304-4238/87/$03.50
© 1987 Elsevier Science Publishers B.V.
302
( Synge, 1969). The bulbs are cultivated for their fragrant white or, in H. amancaes and H. × spofforthiae, yellow flowers. Species noted in commerce include H. amancaes, H. harrisiana, H. littoralis and H. speciosa, along with the following hybrids ofH. narcissiflora: Hx[estalis, together with the selection Zwanenburg (hybrid with H. longipetala); H. X macrostephana forms 'Daphne' and 'Advance' (with H. speciosa); H. 'Sulphur Queen' (H. ×spofforthiae) (with H. amancaes ). The sub-genus Ismene ( H. amancaes, H. narcissiflora and H. pedunculata) is characterized by a staminal cup longer than the inflexed filaments. The sub-genus Hymenocallis has the staminal cup shorter than or subequal to the erect spreading filaments (Synge, 1969). Traub (1962, 1963) recognised four s u b - g e n e r a - HymenocaUis (s.s.), Elisena, Pseudostenomesson and Ismene m but he and other students of the group (e.g. Flory, 1976) retained HymenocaUis as the generic name, and Ismene was included under HymenocaUis by K.A.V.B. (1963). On the other hand, Sealy (1954) restricted his monograph to Hymenocallis s.s.. On the basis of cultural requirements and geographical distribution, the designation Ismene seems useful; plants in this group may be grown (in the U.K. ) outdoors in a sheltered position, and occur, along with Elisena and Pseudostenomesson, in South America, rather than in North America and the West Indies as does Hymenocallis s.s.. The Old-World genus Pancratium is distinguishable from HymenocaUis by the many ovules in each loculus. The large dry dormant bulbs of Hymenocallis are sold in winter and spring either for forcing into bloom in April-May or, in the case of the Ismene subgenus, for growing in a sheltered outdoor position. Species of HymenocaUis s.s. are regarded either as evergreen stove plants (e.g.H. speciosa) or deciduous glasshouse plants (e.g.H. harrisiana) (Synge, 1969). Hymenocallis is a very minor component of the bulb trade, with some 24 000 bulbs imported to The Netherlands in 1980-1981 (Anon., 1982), but the showy, fragrant inflorescences coupled with the vigorous growth of the hardier species hint at the potential value of the genus (Fig. 1 ). Observations of a small stock of H. ×[estalis, maintained at the Glasshouse Crops Research Institute (G.C.R.I.) for a number of years, contributed to this impression, and prompted the trials described in the present paper. The effects of bulb grade, storage temperature and duration, growing conditions, growth retardants and hot-water treatment on flowering performance, and of bulb grade, cultural conditions and planting rate on bulb yields were examined. MATERIALS AND METHODS
Stock bulbs of Hymenocallis Xfestalis (Worsley) hort. were grown individually in 19-cm-diameter pots of G.C.R.I. 2:1 mix (peat/sand compost (3:1 v/v) and John Innes No. 2 compost, 2:1, v/v) in a glasshouse at a minimum maintained temperature of 16°C and ventilated at 18°C. From 1979, stocks were
303
(a)
(b) Fig. 1. The growing plant (a) and a single flower (b) of Hymenocallis×festalis. Photograph G.C.R.I.
304 also grown in ridges in the field at Littlehampton, on soil of the brickearth type. Stocks were planted in April, and dried off in pots or lifted from the field in October. After cleaning and cutting off leaves (but leaving the root systems undamaged), bulbs were dipped at ambient temperatures for 3 h in 0.05% a.i. lindane (as Lindex Miscible 10% ) with 0.1% wetter (PBI Spreader) followed by 30 rain in 0.2% a.i. benomyl (as Benlate 50% W.P. ) with 0.5% a.i. captafol (as Sanspor 50% ) and 0.1% wetter to control bulb fly and red spot disease (Stagonospora curtisii), respectively. Bulbs were then dried and stored at ca. 17°C. Details of individual experiments are given under Results. H.W.T., used to control a variety of bulb pests including bulb fly, and combined with a fungicidal treatment, consisted of a 3-h dip at 44 °C in 0.2% a.i. benomyl (as Benlate 50% W.P.) and 1.0% a.i. dithiocarbamate (as Maneb 80% W.P.). Growth retardants were diluted from stock solutions of ancymidol (Lilly Research Centre), ethephon (as "Ethrel-E", 2-chloroethylphosphonic acid) ( I.C.I. Plant Protection Division) and chlormequat chloride (as "3C Cycocel" ) (Applied Horticulture). In assessing flowering performance, the following records were routinely made: glasshouse period (days in the glasshouse until opening of the first floret), scape length (bulb tip to base of pedicel), first floret size (maximum diameter of the staminal cup), and floret number. For the growth-regulator experiment, stem length was measured when treatments were applied, and used as a co-variate to adjust subsequent data. Where S.E.D.'s are quoted for experiments with variable replication, these are the values for comparisons between a treatment having the minimum number of replicates and one with the maximum number. RESULTS
Aspects of flowering performance Bulb grade, m Glasshouse-raised bulbs, grades 9-10 up to 18-19 cm circumference, were stored at ca. 17°C from lifting until planting and transfer to the glasshouse on 15 April 1981. Flowering performance is shown in Table I. Only 25% of bulbs in the smallest grade (9-10 cm) produced flowers, but at least 90% did so in bulbs larger than 13 cm. Glasshouse period was slightly longer in the larger grades (43 days in the smaller grades, 49 days in the largest). Scape length increased steadily with increasing bulb size, from 371 to 545 ram. There were no significant effects of bulb grade on floret size, but floret number increased with bulb size, from about 2 in the smaller grades to 7 in the largest. To obtain an average of 4 florets, a bulb of at least 13 cm circumenference was needed. The mean number of emerged leaves per plant at anthesis was 7-8.
305 TABLE I Flowering performance of 10 grades of glasshouse-grown bulbs of replicates of each grade (15 for 18-19 cm)
HymenocaUis. Figures
are means for 20
Bulb grade (cm circumference)
Plants reaching anthesis (%)
Glasshouse period (days)
Stem length (ram)
First floret size (ram)
Floret number
Leaf number
9-10 10-11 11 - 12 12-13 13-14 14-15 15-16 16-17 17-18 18-19
25 70 80 80 90 100 95 95 100 100
43.3 43.1 43.4 42.2 43.7 42.7 44.8 44.7 49.2 48.9
371 368 403 407 424 430 451 501 518 545
31.5 30.4 30.3 31.1 31.4 30.4 30.8 31.1 31.5 31.8
2.3 2.1 2.9 3.4 4.0 4.7 5.6 5.5 6.3 7.2
6.8 6.8 7.4 7.2 7.3 7.3 8.0 7.5 7.6 7.5
0.52
0.35
S.E.D.
2.14
26.4
1.09
Temperature of bulb storage. ~ Field-raised bulbs of grades 12-14, 14-16 and
16-18 cm circumference were stored at 5, 17 or 20 °C from lifting until planting and transfer to the glasshouse on 21 April 1982. Flowering performance is shown in Table II. In contrast to the glasshouse-grown bulbs of the previous experiment, a lower percentage of bulbs flowered, and these had smaller numbers of florets. Overall, 35% of bulbs reached anthesis following 5 ° C-storage, and about 70% following 17 or 20 ° C-storage, the remainder of the plants remaining vegTABLE II Flowering performance of 3 grades of bulbs of Hymenocallisfollowing storage at different temperatures. Date based on 20 replicate bulbs for each treatment combination
Bulb grade (cm circum-
Storage temperature
Plants reaching
Glasshouse period
Stem length
First floret
ference)
( °C )
anthesis ( % )
(days)
(ram)
size ( m m )
12-14
5 17 20
15 65 90
109.5 36.9 28.7
810 347 331
35.5 32.2 32.0
2.5 2.4 2.2
14-16
5 17 20
50 90 75
108.6 37.1 29.4
765 349 340
32.0 31.9 32.4
2.4 2.7 2.7
16-18
5 17 20
40 60 45
103.6 38.4 30.2
753 374 355
29.0 31.8 32.2
2.4 4.0 4.0
S.E.D.
2.69
34.5
1.23
Floret number
0.55
3O6 TABLE III Flowering performance of field-grown 14-16-cm Hyrnenocallis bulbs following storage for various durations at 17 ° C. Data based on 20 replicate bulbs for each treatment combination Date of end of storage
Plants reaching anthesis ( % )
Glasshouse period
Stem length (ram)
First floret size (mm)
Floret number
378 349 349
35.1 31.9 29.7
2.5 2.7 2.8
(days) 23 February 21April 15 June S.E.D.
85 90 90
71.4 37.1 22.5 1.55
13.9
0.60
0.25
etative. Floret number reached 4 in the largest grade of bulbs (16-18 cm) following storage at 17 or 20°C, and was ca. 2.5 in other cases. Glasshouse period and stem length decreased with increasing storage temperature, with no effect of bulb grade or interaction between the factors. After 5 ° C-storage, glasshouse period was very prolonged and stems very long (107 days and 767 m m overall), compared with values of 29 days and 339 m m for bulbs stored at 20 ° C. First floret size showed no effect of bulb size following 17 or 20 ° storage, although it fell with increasing bulb size after 5 ° C-storage. Duration of bulb storage. ~ Field-raised bulbs, grade 14-16 cm, were stored at 17°C until planting and transfer to the glasshouse on 23 February, 21 April and 15 June 1982. The results are shown in Table III. The percentage of bulbs reaching anthesis, and the number of florets, were in conformity with the results of the previous experiment, and were unaffected by storage duration. Glasshouse period, stem length and first floret size all fell following longer storage; there was a marked effect of delaying planting from February to April, and a smaller effect of a further delay until June. Performance of glasshouse- and field-raised bulbs. - - Bulbs of grade 14-16 cm, raised in the glasshouse, were re-planted in April 1983 either in the glasshouse or in ridges in the field. They were lifted in October, stored at 17 ° C until April 1984, and then both batches were grown in the glasshouse. Flowering performance was assessed in each year, and is shown in Table IV. Bulbs grown initially in the field or glasshosue had equal floret sizes and numbers, but anthesis was earlier and stems longer in the glasshouse. In the next year, when both lots were grown in the glasshouse, the ex-field bulbs flowered earlier and with shorter stems, but bore larger and distinctly more florets (see also the section on bulb growth under glass and in the field, below). Effects of growth retardants, m Field-raised bulbs, grade 16-18 cm, were planted in the glasshouse in April 1982. On 2 June (average stem length 103 ram), 300
307 TABLE IV Flowering performance of glasshouse-raised bulbs of HymenocaUis (A) in the field or glasshouse in 1983, and (B) of these bulbs grown in the glasshouse in 1984. Means based on 30 plants each Cultural conditions
(A) Ex-glasshouse Field Glasshouse S.E.D. (B) Glasshouse Ex-field Ex-glasshouse S.E.D.
Plants reaching anthesis ( % )
Time to anthesis (days)
Stem length (ram)
First floret size (ram)
Floret number
97 100
39.6 16.5 0.98
400 544 10.5
30.0 30.4 0.40
5.1 4.9 0.24
97 90
21.5 35.9 0.82
539 576 16.2
32.0 30.0 0.42
5.8 3.7 0.30
ml per pot compost drenches were given, and further watering was subsequently restricted for 3 days, the plant pots being placed on "saucers" for the whole of this period. The treatments consisted of ancymidol (1.25, 2.5 or 5.0 mg a.i. per pot), ethephon (960 or 1920 mg a.i. per pot) and chlormequat chloride ( CCC ) ( 2500 or 5000 mg a.i. per pot); controls received plain water. Ethephon delayed anthesis by 3-6 days compared with controls; ancymidol and chlormequat had no effect ( Table V). Ancymidol and chlormequat ( at all concentrations tested) reduced stem length by ca. 10% while ethephon at 960 TABLEV Effect of growth r e t a r d a n t t r e a t m e n t s on flowering performance of HyrnenocaUis bulbs. Five replicate bulbs per t r e a t m e n t , data are m e a n s of t h e indicated n u m b e r of bulbs reaching a n t h e s i s
Treatment (raga.i.per pot)
Number of plants reaching anthesis
Glasshouse period (days)
Stem length (mm)
Control
5
51.5
490
Ancymidol 1.25 2.50 5.00
4 5 5
52.8 51.3 51.1
451 454 453
E t h e p h o n 960 1920
5 5
57.2 54.5
385 250
Chlormequat 2500 5000
4 5
51.5 52.4
455 442
S.E.D.
1.24
28.3
308 and 1920 mg a.i. per pot reduced length by 21 and 49%, respectively. There were no significant effects of retardants on first floret size or floret number, which averaged 31.0 m m and 3.8, respectively, and no adverse effects of retardants on flower or plant quality were seen.
Effect of date ofH. W. T. m Field-raised, 17 oC-stored 10-12-cm bulbs were subjected to H.W.T. and bulb dissection to determine I.S.D. at monthly intervals from 2 November 1982 to 21 March 1983. A further batch of bulbs remained untreated. All treated bulbs were planted and transferred to the glasshouse on 19 April 1983. Bulb I.S.D.'s at treatment, and the subsequent flowering performance of the treated bulbs (including an assessment of H.W.T. damage to the florets), are given in Table VI: Except when the treatment was given at the last date, when perianth and androecium initials were already well formed, H.W.T. resulted in fewer plants reaching anthesis, in damaged, small florets, and lower floret numbers. There were no clear effects on anthesis date. Floret damage, which was extensive following H.W.T. between 7 December and 14 February, took the form of deformation of the perianth accompanied by, at later dates, damage to the androecium. Earliest H.W.T. (2 November) resulted in little floral damage in those plants reaching anthesis, although this number was reduced to 65%. H.W.T. at the latest date (21 March) resulted in no obvious damage; flowering performance being similar to that of the untreated controls. Aspects of bulb yields Bulb growth under glass and in the field, m Glasshouse-raised bulbs, grade 14-16 cm, were stored at 17°C after lifting and then planted in April 1983 either in the glasshouse or in ridges in the field (30 bulbs each). After one season's growth, mean whole bulb weights (including main bulb and offsets) were similar in either case (227 and 230 g). However, although the mean grades of the main (central) bulb were also similar (16-17 cm circumference), a greater proportion of the total weight of the glasshouse-grown bulbs was due to offset production. In a further trial, field-raised bulbs of grades 10-12 and 12-14 cm were stored over winter at 17 ° C and planted in April 1983 either in the 16 °C glasshouse or in a cold glasshouse ( m i n i m u m maintained temperature 5 ° C, ventilated at 10 ° C). To simulate different durations of growing season, leaves were removed and bulbs lifted and dried on 4 dates (30 August, 13 September, 27 September or 11 October). Bulb grade (main bulb) and bulb weights (main bulb and offsets) were then determined. Prolonging the growing season enhanced the growth of the main bulb and offsets, and growth was somewhat better in the cool glasshouse than in the warm glasshouse (Fig. 2 ). The analysis of variance indicated that there were no interactions between planted bulb grade, glasshouse temperature and length of growing season, hence the marginal or overall
Sp P A
G G or C (C) 3
2 Nov. 7 Dec. 10 Jan.
14 Feb. 21 Mar. None
75 95 95
65 50 45
Plants reaching anthesis ( %)
1.21
51.5 50.7 52.8
51.7 48.4 53.2
Glasshouse period (days)
28.4
433 458 424
417 268 281
Stem length (ram)
2.26
28.3 30.9 30.7
31.2 27.5 26.0
First floret size 2 (ram)
0.29
2.1 2.9 2.7
2.3 1.6 2.2
Floret number
87 0 0
15 100 100
(%)
Flowering plants with damaged florets
Split stamina] cup Perianth deformed in all florets Perianth deformed in all florets; some anthers deformed Ditto None None
Floral damage
1Sp = spathe initial visible; P = perianth segment initials visible; A = androecium initials visible; G = gynoecium initials visible; C = staminal cup initials visible. 2For 7 Dec. to 14 Feb. treatments, floret sizes based on reduced number of replicates because of extensive floret deformity. 3Determined at planting.
S.E.D.
I.S.D. of first floret at H.W.T.~
Date of H.W.T. (1982/83)
Effects of H.W.T. of Hymenocallisat various stages of floral development on floret damage and other aspects of flowering performance. Means for flowering performance based on 20 bulbs each. I.S.D.'s based on 10 bulbs each
TABLE VI
310
18f
16
i
L~
ill
Z
200 W h o l e bulb
I
180
IMainbu,b
o) 160
T
J~ J~
I
Z
140
E
.?.
i
.m
.2
#
T
IO0
i 8O
Bulb g r a d e
(cm)
Glasshouse temp. ( ° C )
D a t e of d r y i n g - o f f bulbs
Fig. 2. Effect of bulb grade (cm circumference) at planting, glasshouse temperature (minimum ° C/ventilation ° C) and date of drying-off bulbs on weight of main bulb and whole bulb cluster, and grade of main bulb of harvest. Data are marginal means for the three factors, based on 10 replicate bulbs for each treatment combination. Vertical bars are S.E.D.'s.
means for the three factors are shown. In the best conditions (cool glasshouse, grown until October) a 10-12-cm bulb yielded a 17-cm-circumference bulb weighing 121 g and a 12-14-cm bulb yielded an 18-cm bulb weighing 147 g; comparable values for warm glasshouse bulbs were 17 cm, 116 g (for a 10-12cm bulb planted) and 19 cm, 149 g ( for a 12-14 cm bulb planted). Glasshousegrown bulbs produced numerous offsets. Bulb planting grade and planting rate. ~ Field-raised bulbs of grades 6-8, 8-10, 10-12 and 12-14 cm circumference were planted outside in a bed in April, in weighed, counted lots, in 1-m rows 30 cm apart, at planting rates corresponding to 350, 700 and 1050 g of bulbs m - 1. Each grade-rate combination was duplicated in two plots, being randomly allocated within plots, and with guard plants at the extremities of the plots. The trial was repeated in two growing seasons (1981 and 1982). In September, bulbs were graded and the number and weight
311
1981
1.5
Grade (cm) planted - - o - - 6-8 ---A---•- - ' 0 " - - "
---V---
--
o
1982 ~
8-10 10-12
--
A ,.~ .~
12-14
¢u c
o
.¢: .2
1.0
o --'.'-.~ .-~.... o.__
I
--v
. . . .
=-----.~.---v I
5 o
0.5
I
35O
I
I
I
700
1050
350
1 700
I 1050
Plantingrate ( g / m ) Fig. 3. Bulb yields (expressed as log, of final weight divided by planted weight ) in Hymenocallis bulbs of 4 grades grown at 3 planting rates (weight of bulb per metre run) in two seasons. Values are means of duplicate plots for each year. Vertical bars are S.E.D.'s.
of bulbs in each grade were recorded. Bulb growth was greater in 1982 than in 1981, with a more marked decline in bulb growth with increased planting rate in the lateryear (Fig. 3 ). There was a significanteffectof planted bulb sizeon weight increase:in 1981 there was an overallincrease (across allplanting rates) of 220% for 12-14-cm bulbs, increasing to 290% for 6-8-cm bulbs, with corresponding figures of 265 and 330% for 1982. Only the larger grades of bulbs produced offsets.In 1982, for example, bulb numbers increased by 140% in the 12-14-cm planted grade, with no effectof planting rate. DISCUSSION
Our observations confirmed H. X[estaliz as a highly attractive and vigorous ornamental. There appears to be no detailed information on the horticultural performance of Hymenocallis available in the literature, so the findings summarised below should provide guidelines for potential growers of this crop. A major consideration is that individual florets are relatively short-lived, so that large bulbs are needed to obtain a satisfactory floret number to extend the flowering period. In a 16°C-glasshouse, successive florets open at 1-2 day intervals, each floret remaining in reasonable condition for 2-3 days. Floret number increased markedly in the larger bulb grades: in one trial with glasshouse-raised bulbs, floret number increased from 2 (for a 9-10-cm bulb) to 7 (18-19-cm bulb), but field-raised bulbs of the same sizes produced fewer florets. Generally, bulbs greater than 13-cm-grade flowered reliably, but to ensure at least a reasonable floret number (4), a bulb of 16-18 cm should be used. Planting bulbs in the glasshouse relatively early (February) led to greater
312 flower size compared with bulbs planted in April-June, but the time in the glasshouse to anthesis was prolonged. Later anthesis could be achieved by delaying planting until June (anthesis in 3 weeks), or by storing bulbs over winter at a low temperature. However, the latter also greatly reduced the percentage of bulbs which flowered. Flower quality of both glasshouse- and fieldgrown bulbs were similar, but stems were longer in the former. The stems of HymenocaUis, which are excessively tall for pot-plants, were successfully dwarfed by compost-drenching with ethephon, with no adverse effectson flower quality: ancymidol and chlormequat had only slight effects on stem length at the concentrations used. H.W.T., if required as a pest and disease control measure, did not damage florets if given shortly before planting, when the staminal cup initialwas visible upon bulb dissection. Bulb growth was more vigorous when plants were grown in the field than in the glasshouse, and it appeared that a long growing season is important in obtaining large bulbs capable of forming a satisfactory number of florets.Outdoors, the growing season was limited by the onset of frost, but an early light frost damaged only the foliage. In the glasshouse, but not in the field,copious offset bulbs were produced, perhaps because of higher temperatures around the bulb. In bulbs grown in beds, although bulb growth differed from year to year, weight increases of 200-300% were obtained. Lower planting rates (350 g m -I) were especially beneficial for the smaller grades of bulbs. Some practical problems were encountered in growing the Hymenocallis stock. The large, fleshy contractile roots cause difficultyin cleaning bulbs and in liftingfrom the field,when the basal plate of the bulb can easilybe damaged (deep planting should be avoided). Some problems were encountered with leaf scorch or red spot disease ( Stagonospora curtisii) and large bulb-fly (Merodon equestris), but these were controlled by the measures used. Vegetative propagation of H. ×[estalis should present few problems. Numerous offsets are produced by pot-grown plants cultured in the glasshouse, and it may also be propagated easily by the "twin-scaling" technique (G.R. Hanks, unpublished data, 1982 ). The large photosynthetic seeds of HymenocaUis have attracted some attention (Whitehead and Brown, 1940; Flint and Moreland, 1943 ). Under our conditions few seeds were set, but the seedlings were vigorous, producing flowering-size bulbs in about 3 years. The present G.C.R.I. stock of H. ×festalis was confirmed as such by reference to the descriptions given by Synge (1969) and by chromosome counts in Feulgens and aceto-carmine root-tip preparations (see Flory, 1976). In our stock, 2n=ca. 64; Flory (1976) gives H. ×festalis as 2n=62-64, with the parents H. narcissiflora (H. calathina ) and H. longipetala (Elisena longipetala ) with 2n= 104-110 and 50, respectively. Flory (1976) listed somatic chromosome numbers for over 100 accessions of Hymenocallis ranging from 38 to 110, with a further single accession having 2n= 195; he noted, in several taxa, differences in chromosome numbers between different accessions of the same
313 taxon. Several hybrids are known, and hybridization occurs freely, both within and between the sub-genera (e.g. see Raina and Khoshoo, 1971 ). This genetic diversity and ease of hybridisation make Hymenocallis breeding an attractive proposition, while the discovery of new species adds to these resources; for example, a new species H. heliantha ( sub-genus Ismene), with potential in its large yellow flowers and small plant size, has recently been described (Ravenna, 1980). Even with the present species and hybrids there is clear potential for the greater horticultural exploitation of Hymenocallis. A wider market for plants like H. ×festalis, sold as a large prepared bulb complete with pot and compost, like Hippeastrum, is suggested. ACKNOWLEDGEMENTS We thank Lilly Research Centre for a gift of ancymidol, A.A. Tompsett (Rosewarne Experimental Horticulture Station) for information on bulb dip and H.W.T. treatments, and F.A. Langton and R. Menhenett for valuable comments on the text.
REFERENCES Anonymous, 1982. Invoer bloembollen in Nederland. Bloembollencultuur, 93: 91. Flint, L.H. and Moreland, C.F., 1943. Note on photosynthetic activity in seeds of the spider lily. Am. J. Bot., 30: 315-317. Flory, W.S., 1976. Distribution, chromosome numbers and types of various species and taxa of Hymenocallis. Nucleus, 19: 204-227. K.A.V.B. (Koninklijke Algemeene Vereeniging voor Bloembollencultuur), 1963. Classified list and internationalregisterof hyacinths and other bulbous and tuberous rooted plants.K.A.V.B., Haarlem, 214 pp. Raina, S.N. and Khoshoo, T.N., 1971. Cytogenetics of the tropicalbulbous ornamentals. V. Chromosomal variation and evolution in Hymenocallis. Cellule,68: 239-259. Ravenna, P., 1980. A new yellow-floweredHymenocaUis (Amaryllidaceae) from North Peru. Bot. Not., 133: 97-98. Sealy, J.F., 1954. Review of the genus Hymenocallis. Kew Bull.,2: 201-240. Synge, P.M., 1969. Supplement to the Dictionary of Gardening. Clarendon Press, Oxford, pp.
358-360. Traub, H.P., 1962. Key to the subgenera,alliances and species of Hymenocallis. Plant Life, 18 (The AmaryllisYearBook): 55-72. Traub, H.P., 1963. Generaof Amaryllidaceae.The AmericanPlant Life Society,La Jolla, CA, 85 PP. Whitehead, M.R. and Brown, C.A., 1940. The seedof the spider lily, HymenocaUisoccidentalis. Am. J. Bot., 27: 199-203.