- Email: [email protected]
Colonization of freshly abscissed and decaying leaves by aero-aquatic hyphomycetes
Trans. Br, mycol. Soc. 73 (1) 99-102 (1979)
Printed in Great Britain
COLONIZATION OF FRESHLY ABSCISSED AND DECAYING LEAVES BY AERO-AQUATIC HYPHOMYCETES By P. J. FISHER Department of Biological Sciences, University of Exeter
At a eutrophic site, aero-aquatic fungi colonized freshly abscissed beech leaves in preference to decaying leaves. At a oligotrophic site Helicodendron triglitziense and Papulospora sp. preferentially colonized freshly abscissed leaves whilst two other species showed no significant preference for either substrate. In a similar experiment Hi fractum (a species from needles and cones in oligotrophic habitats), colonized leached pine needles in preference to beech leaves at the oligotrophic site but did not colonize beech leaves or needles at the eutrophic site. In a laboratory experiment H. triglitziense and H. giganteum colonized sterilized and unsterilized freshly abscissed beech leaves, and sterilized decaying leaves, in preference to unsterilized decaying leaves. Comparatively little is known about natural substrates colonized by aero-aquatic hyphomycetes. Linder (1929) mentions decaying Salix twigs, catkins of Alnus and decaying coniferous wood. Glen-Bott (1951, 1955) recovered Helicodendron conglomeratum and H. giganteum from submerged decaying leaves of beech and oak, noting that aero-aquatic fungi are found most frequently on black decaying leaves. Fisher (1977) found that certain aero-aquatic hyphomycetes colonized freshly abscissed beech leaves under micro-aerobic and anaerobic conditions in their natural habitat and that this ability was greatly increased by higher oxygen tensions in the water. The experiments described in this paper were designed to investigate whether freshly abscissed or black decaying beech leaves, as well as freshly abscissed or leached pine needles are more readily colonized by selected aero-aquatic hyphomycetes. The experiments were conducted during MarchApril 1977 at a depth of 15-20 em, in a water filled channel about 600 m long by 2-6 m wide at Stoke Woods, South Devon, where conditions are eutrophic during most parts of the year, and in Bystock Reservoir, South Devon, where conditions remain oligotrophic throughout the year (Table 1).
MATERIALS AND METHODS
The following species were simultaneously investigated at Stoke Woods and Bystock: Clathrosphaerina zalewskii Beverwijk, Helicodendron giganteum Glen-Bott, Hi fractum Fisher, H. triglitziense (Jaap) Linder and Papulospora sp. Laboratory and field observations suggested
that underwater spread by these fungi is often brought about by leaf to leaf contact and by mycelial fragments. Pure mycelium mixed with quartz sand was therefore used as inoculum for all underwater experiments. Freshly abscissed beech leaves (Fagus sylvatica) will be referred to as 'brown leaves' and decaying beech leaves as 'black leaves'. Brown leaves were stripped from the trees the previous autumn and stored at -10°C. Black leaves were recovered from below the water surface at Stoke Woods and sorted by holding them in front of a 60 W electric light bulb. Leaves from the previous autumn usually transmit some light and retain traces of autumn colour while older leaves are opaque. Only opaque leaves were chosen for the experiment, but leaves which had become slimy and showed signs of disintegration were excluded. Leaf disks, 3'6 mm diam, were used throughout; about 6000 unsterilized disks of each kind served as the stock from which all those for the experiments were taken. For the experiments with Helicodendronfractum leaf disks of both kinds as well as 6 rom length of pine needles from Pinus sylvestris were used. Pine needles were of two types; freshly abscissed brown needles stripped from trees and identical needles leached by submersion underwater in 1 rom mesh nylon bags at Stoke Woods for 18 months prior to the experiment. Assays to establish what natural colonization by aero-aquatic. fungi had occurred on black disks and leached pine needles whilst in the water were conducted on 300 black disks randomly chosen from stock and on 50 leached pine needle segments chosen from a stock of 1000.
0001-1536/79/2828-5270 $01.00 © 1979 The British Mycological Society
Aero-aquatic Hyphomycetes
100
Table 1. Water characteristics mg 1-1 Stoke Woods (SW) and Bystock (B) during periods of drought and flooding Drought (1976)
(% saturation)
Biological oxygen demand
Nitrogen as N
~
~
~
O.
April May June July
Temp. CC)
pH
~
~
SW
B
SW
B
SW
B
SW
B
SW
B
10
11
11
16 20
13 17 22
7'2 7'3 7'6 7"3
7'5 7'7 7"4 7'2
0'9 0'0 0'0 0'0
82 87 80 82
15'0 30'0 59'0 28'0
1,6 1'4 1'2 1'0
1'12 9'5 0 36'05 56'00
1'4 1,6 1'2 1'7
8 8
7 7
7'3 7'3
7'2 7'2
99 97
1'3 1,6
1'1 1'2
2'3 8 2'02
1'03 1'03
Flooding (1977) March April
84 83
Each fungus to be investigated was grown in a beech leaf decoction, the mycelium collected, homogenized in an M.S.E. Omnimixer and thoroughly mixed with 300 g of sterile quartz sand to form an inoculum. Twenty cm3 of each inoculum was placed in Petri dishes (5 cm diam), and 60 brown leaf disks or 60 black leaf disks per dish were buried evenly in the inoculum. For H. fractum 60 1 em units of leached or fresh pine needles were similarly buried. Petri dishes were placed in plastic trays and submerged in equal numbers at the field sites. Flooding at Stoke Woods during the experiments deposited a 3 mm layer of mud on the Petri dishes. In a similar laboratory experiment, colonization by H. giganteum and H. triglitziense of black and brown unsterilized leaf disks was compared with disks sterilized by gamma radiation from a Cobalt source (2 x 10 8 rads). Petri dishes containing the leaf disks and inocula were placed independently in 500 em" beakers and submerged under 10 em of water from Bystock Reservoir and incubated at 10°. After 4 weeks all leaf disks and needles were harvested, washed well in distilled water, and placed on moist filter paper in closed Petri dishes to be incubated for 12 days at 10 ± 2°. Sporulation was used as the criterion for colonization. RESULTS
Table 2 gives the comparison between colonization of black and brown leaf disks at Stoke Woods and Bystock. Table 3 gives the comparison between coloi.ization of black and brown sterile and unsterilized beech leaf disks in the laboratory. Means and deviations have been calculated from three replicates and show the number of leaf baits colonized out of 60. Of 300 black control disks in the field experiment 7% were colonized by H. triglitziense and 3 % by Papulospora sp, before the
start of the experiment. These have been deducted from the results. None of the 50 control pine needles submerged for 18 months at Stoke Woods were colonized by H. fractum. In the laboratory experiment the control disks were found to be uncolonized by the species investigated. The colonization index CI (Tables 2 and 3) represents the ratio of mean number of black leaf disks to mean number of brown leaf disks colonized by each species. DISCUSSION
Comparisons between colonization of leaf baits at Stoke Woods and Bystock show that at the eutrophic site at Stoke Woods brown leaf disks were more readily colonized than black leaf disks by all fungi. At the oligotrophic site at Bystock H. giganteum and C. zalewskii colonized brown and black leaves equally effectively. The following reasons are suggested for these results. Typical terrestrial species, present in freshly abscissed leaves become relatively inactive under water (Barlocher & Kendrick, 1974) providing relatively little competition to the aero-aquatic fungi. Black leaves, however, that have been in the water for 6 months or longer are likely to be colonized by numerous aquatic micro-organisms which could provide active competition to the inoculum species, especially for oxygen (Fisher, 1977). Sanders & Anderson (1979) also showed that colonization of wood blocks by aquatic hyphomycetes is closely related to the size of the available resources and that other species are excluded once the characteristic species assemblage is established. Throughout the 1977 experiments at Stoke Woods oxygen tension in the water was about 15 % lower than at Bystock (Table 1) and the supply of oxygen to the leaf disks at Stoke Woods was further reduced by a layer of mud which formed on the
P.J. Fisher Table
2,
101
Comparisons between colonization of black and brown leaf disks in the field (means of three
replicates Stoke Woods
Bystock , Blackleaves Brown leaves Indigenous I
Black leaves H elicodendron triglitziense
7'1 ±2's
Brown leaves Indigenous
CI* 0'2
3s'3±4'2
30'4±7's
Introduced H, giganteum
23'7±3'1
s6'3±3'8
0'4
6o'o±0
0'06
eo-c j o
Introduced Clathrosphaerina zalewskii
2'8±3'4
47'3±4'7
Indigenous Papulospora sp, H elicodendron fractum
8'9±1's 0'0
4 1'7±s'o 0'0
Fresh pine
Leached pine
0'0
0'2 0'0
Fresh pine 0'0
0'0
7's±4'2 0'0 0'0
6o±0
Indigenous NS s9'7±O'6 Indigenous NS 6o±0 Indigenous 25'3 ±8'1 9'7±4's
CI 0'5 1'0 1'0 0'3 0'0
Leached pine 20'O±3'6
0'0
P < 0'05 except where indicated by NS (not significant),
mean number of black leaf disks colonized * Colonization Index (CI) = mean number of brown leaf disks colonized'
Table 3. Comparison between colonization of sterile or non-sterile black and brown leaf disks in the laboratory (means of three replicates) Sterile
Helicodendron triglitziense H, giganteum
Unsterilized
Black
Brown
CI*
Black
Brown
CI
21'2±7'6 46'4 ± 6'9
s6'4±3'2 60'0 ± 0'0
0'4 0,8
0'0 15'2 ± 8'2
47'3±6'9 60'0 ± 0'0
0'0 0'3
P < 0'05 when sterileor non-sterile blackdisksof each species are comparedwith their respectivebrown disks. and when black sterile and non-sterile disks are compared with each other. mean number of black leaf disks colonized * Colonization Index (CI) = mean number of brown leaf disks colonized'
Petri dishes. A greater oxygen supply in the littoral zone of the oligotrophic habitat at Bystock probably allowed certain of the aero-aquatic fungi, i.e, H. giganteum, H. triglitziense and C. zalewskii to compete more effectively against the established micro-flora of the decaying leaves, While an adequate supply of oxygen is probably the most important single factor which determines the frequency and distribution of these organisms in static water. other aspects of antagonistic microbial activity in decaying leaves may also play an important role in determining colonization patterns. These observations are supported by a comparison between colonization of sterile and non-sterile black disks in a laboratory experiment (Table 3) where it was shown that black sterile disks were more readily colonized than non-sterile ones when supplies of oxygen were similar. H. fractum colonized leached pine needles more effectively than beech leaves. This may explain
why this fungus is abundant at Bystock where pine needles form the greater part of the leaf litter. The absence of this species from Stoke Woods may be explained by its apparent inability to colonize black decaying leaves in competition with other micro-organisms andthe absence of suitable pine needle substrates there. This species has been recovered on numerous occasions from oligotrophic sites in Great Britain but appears to be absent from eutrophic habitats (Abdullah, Fisher & Webster, 1979). The colonization index (Cf) (Tables 2 and 3) represents the ratio colonized black disks : colonized brown disks and can give an indication of the saprophytic competitive ability of aero-aquatic hyphomycetes in a particular situation. Thus a high colonization index of 1'0 for H. giganteum and C. zalewskii at Bystock means equally effective colonization by the fungi of black and brown leaves, inferring high saprophytic competitive
Aero-aquatic Hyphomycetes
102
ability in that situation. Low colonization indices of 0 '4 and 0'06 for the same fungi at Stoke Woods suggest lower saprophytic competitive ability at the eutrophic site. In the field experiments freshly abscissed leaves were more readily colonized than decaying leaves. Yet when leaves are recovered from Stoke Woods black leaves are frequently colonized by aeroaquatic fungi while brown leaves are not. This may be explained by a time factor. Black leaves remain in the water from 8 months to 3 years while freshly abscissed leaves remain in the brown state for only 7-8 months. The time available for colonization of black leaves therefore exceeds that for brown leaves by four to five times. REFERENCES
P. J. & WEBSTER, J. (1979). Two new species of aero-aquatic hyphomycetes. Transactions of the British Mycological Society 72, 3 24--329.
ABDULLAH,
S. K.,
FISHER,
BARLOCHER, F . & KENDRICK, B. (1974). Dynamics of the
fungal population on leaves in a stream. Journal of Ecology 62, 761-791FISHER, P. J. (1977). New methods of detecting and studying saprophytic behaviour of aero-aquatic hyphomycetes from stagnant water. Transactions of the British Mycological Society 68, 407-411GLEN-BOTT, J. I. (1951). Helicodendron giganteum n.sp, and other aerial sporing hyphomycetes of submerged dead leaves. Transactions of the British Mycological Society 34, 275-279. GLEN-BOTT, J. I. (1955). On Helicodendron tubulosum and some similar species. Transactions of the British Mycological Society 38, 17-30. LINDER, D. H . (1929). A monograph of the helicosporous fungi imperfecti. Annals of the Missouri Botanical Gardens 16, 227-388. SANDERS, P. J. & ANDERSON, J. M. (1979). Colonization of wood blocks by aquatic hyphomycetes, Transactions of the British Mycological Society 73, 10310 7.
(Accepted for publication 8 November 1978)
Printed in Great Britain
COLONIZATION OF FRESHLY ABSCISSED AND DECAYING LEAVES BY AERO-AQUATIC HYPHOMYCETES By P. J. FISHER Department of Biological Sciences, University of Exeter
At a eutrophic site, aero-aquatic fungi colonized freshly abscissed beech leaves in preference to decaying leaves. At a oligotrophic site Helicodendron triglitziense and Papulospora sp. preferentially colonized freshly abscissed leaves whilst two other species showed no significant preference for either substrate. In a similar experiment Hi fractum (a species from needles and cones in oligotrophic habitats), colonized leached pine needles in preference to beech leaves at the oligotrophic site but did not colonize beech leaves or needles at the eutrophic site. In a laboratory experiment H. triglitziense and H. giganteum colonized sterilized and unsterilized freshly abscissed beech leaves, and sterilized decaying leaves, in preference to unsterilized decaying leaves. Comparatively little is known about natural substrates colonized by aero-aquatic hyphomycetes. Linder (1929) mentions decaying Salix twigs, catkins of Alnus and decaying coniferous wood. Glen-Bott (1951, 1955) recovered Helicodendron conglomeratum and H. giganteum from submerged decaying leaves of beech and oak, noting that aero-aquatic fungi are found most frequently on black decaying leaves. Fisher (1977) found that certain aero-aquatic hyphomycetes colonized freshly abscissed beech leaves under micro-aerobic and anaerobic conditions in their natural habitat and that this ability was greatly increased by higher oxygen tensions in the water. The experiments described in this paper were designed to investigate whether freshly abscissed or black decaying beech leaves, as well as freshly abscissed or leached pine needles are more readily colonized by selected aero-aquatic hyphomycetes. The experiments were conducted during MarchApril 1977 at a depth of 15-20 em, in a water filled channel about 600 m long by 2-6 m wide at Stoke Woods, South Devon, where conditions are eutrophic during most parts of the year, and in Bystock Reservoir, South Devon, where conditions remain oligotrophic throughout the year (Table 1).
MATERIALS AND METHODS
The following species were simultaneously investigated at Stoke Woods and Bystock: Clathrosphaerina zalewskii Beverwijk, Helicodendron giganteum Glen-Bott, Hi fractum Fisher, H. triglitziense (Jaap) Linder and Papulospora sp. Laboratory and field observations suggested
that underwater spread by these fungi is often brought about by leaf to leaf contact and by mycelial fragments. Pure mycelium mixed with quartz sand was therefore used as inoculum for all underwater experiments. Freshly abscissed beech leaves (Fagus sylvatica) will be referred to as 'brown leaves' and decaying beech leaves as 'black leaves'. Brown leaves were stripped from the trees the previous autumn and stored at -10°C. Black leaves were recovered from below the water surface at Stoke Woods and sorted by holding them in front of a 60 W electric light bulb. Leaves from the previous autumn usually transmit some light and retain traces of autumn colour while older leaves are opaque. Only opaque leaves were chosen for the experiment, but leaves which had become slimy and showed signs of disintegration were excluded. Leaf disks, 3'6 mm diam, were used throughout; about 6000 unsterilized disks of each kind served as the stock from which all those for the experiments were taken. For the experiments with Helicodendronfractum leaf disks of both kinds as well as 6 rom length of pine needles from Pinus sylvestris were used. Pine needles were of two types; freshly abscissed brown needles stripped from trees and identical needles leached by submersion underwater in 1 rom mesh nylon bags at Stoke Woods for 18 months prior to the experiment. Assays to establish what natural colonization by aero-aquatic. fungi had occurred on black disks and leached pine needles whilst in the water were conducted on 300 black disks randomly chosen from stock and on 50 leached pine needle segments chosen from a stock of 1000.
0001-1536/79/2828-5270 $01.00 © 1979 The British Mycological Society
Aero-aquatic Hyphomycetes
100
Table 1. Water characteristics mg 1-1 Stoke Woods (SW) and Bystock (B) during periods of drought and flooding Drought (1976)
(% saturation)
Biological oxygen demand
Nitrogen as N
~
~
~
O.
April May June July
Temp. CC)
pH
~
~
SW
B
SW
B
SW
B
SW
B
SW
B
10
11
11
16 20
13 17 22
7'2 7'3 7'6 7"3
7'5 7'7 7"4 7'2
0'9 0'0 0'0 0'0
82 87 80 82
15'0 30'0 59'0 28'0
1,6 1'4 1'2 1'0
1'12 9'5 0 36'05 56'00
1'4 1,6 1'2 1'7
8 8
7 7
7'3 7'3
7'2 7'2
99 97
1'3 1,6
1'1 1'2
2'3 8 2'02
1'03 1'03
Flooding (1977) March April
84 83
Each fungus to be investigated was grown in a beech leaf decoction, the mycelium collected, homogenized in an M.S.E. Omnimixer and thoroughly mixed with 300 g of sterile quartz sand to form an inoculum. Twenty cm3 of each inoculum was placed in Petri dishes (5 cm diam), and 60 brown leaf disks or 60 black leaf disks per dish were buried evenly in the inoculum. For H. fractum 60 1 em units of leached or fresh pine needles were similarly buried. Petri dishes were placed in plastic trays and submerged in equal numbers at the field sites. Flooding at Stoke Woods during the experiments deposited a 3 mm layer of mud on the Petri dishes. In a similar laboratory experiment, colonization by H. giganteum and H. triglitziense of black and brown unsterilized leaf disks was compared with disks sterilized by gamma radiation from a Cobalt source (2 x 10 8 rads). Petri dishes containing the leaf disks and inocula were placed independently in 500 em" beakers and submerged under 10 em of water from Bystock Reservoir and incubated at 10°. After 4 weeks all leaf disks and needles were harvested, washed well in distilled water, and placed on moist filter paper in closed Petri dishes to be incubated for 12 days at 10 ± 2°. Sporulation was used as the criterion for colonization. RESULTS
Table 2 gives the comparison between colonization of black and brown leaf disks at Stoke Woods and Bystock. Table 3 gives the comparison between coloi.ization of black and brown sterile and unsterilized beech leaf disks in the laboratory. Means and deviations have been calculated from three replicates and show the number of leaf baits colonized out of 60. Of 300 black control disks in the field experiment 7% were colonized by H. triglitziense and 3 % by Papulospora sp, before the
start of the experiment. These have been deducted from the results. None of the 50 control pine needles submerged for 18 months at Stoke Woods were colonized by H. fractum. In the laboratory experiment the control disks were found to be uncolonized by the species investigated. The colonization index CI (Tables 2 and 3) represents the ratio of mean number of black leaf disks to mean number of brown leaf disks colonized by each species. DISCUSSION
Comparisons between colonization of leaf baits at Stoke Woods and Bystock show that at the eutrophic site at Stoke Woods brown leaf disks were more readily colonized than black leaf disks by all fungi. At the oligotrophic site at Bystock H. giganteum and C. zalewskii colonized brown and black leaves equally effectively. The following reasons are suggested for these results. Typical terrestrial species, present in freshly abscissed leaves become relatively inactive under water (Barlocher & Kendrick, 1974) providing relatively little competition to the aero-aquatic fungi. Black leaves, however, that have been in the water for 6 months or longer are likely to be colonized by numerous aquatic micro-organisms which could provide active competition to the inoculum species, especially for oxygen (Fisher, 1977). Sanders & Anderson (1979) also showed that colonization of wood blocks by aquatic hyphomycetes is closely related to the size of the available resources and that other species are excluded once the characteristic species assemblage is established. Throughout the 1977 experiments at Stoke Woods oxygen tension in the water was about 15 % lower than at Bystock (Table 1) and the supply of oxygen to the leaf disks at Stoke Woods was further reduced by a layer of mud which formed on the
P.J. Fisher Table
2,
101
Comparisons between colonization of black and brown leaf disks in the field (means of three
replicates Stoke Woods
Bystock , Blackleaves Brown leaves Indigenous I
Black leaves H elicodendron triglitziense
7'1 ±2's
Brown leaves Indigenous
CI* 0'2
3s'3±4'2
30'4±7's
Introduced H, giganteum
23'7±3'1
s6'3±3'8
0'4
6o'o±0
0'06
eo-c j o
Introduced Clathrosphaerina zalewskii
2'8±3'4
47'3±4'7
Indigenous Papulospora sp, H elicodendron fractum
8'9±1's 0'0
4 1'7±s'o 0'0
Fresh pine
Leached pine
0'0
0'2 0'0
Fresh pine 0'0
0'0
7's±4'2 0'0 0'0
6o±0
Indigenous NS s9'7±O'6 Indigenous NS 6o±0 Indigenous 25'3 ±8'1 9'7±4's
CI 0'5 1'0 1'0 0'3 0'0
Leached pine 20'O±3'6
0'0
P < 0'05 except where indicated by NS (not significant),
mean number of black leaf disks colonized * Colonization Index (CI) = mean number of brown leaf disks colonized'
Table 3. Comparison between colonization of sterile or non-sterile black and brown leaf disks in the laboratory (means of three replicates) Sterile
Helicodendron triglitziense H, giganteum
Unsterilized
Black
Brown
CI*
Black
Brown
CI
21'2±7'6 46'4 ± 6'9
s6'4±3'2 60'0 ± 0'0
0'4 0,8
0'0 15'2 ± 8'2
47'3±6'9 60'0 ± 0'0
0'0 0'3
P < 0'05 when sterileor non-sterile blackdisksof each species are comparedwith their respectivebrown disks. and when black sterile and non-sterile disks are compared with each other. mean number of black leaf disks colonized * Colonization Index (CI) = mean number of brown leaf disks colonized'
Petri dishes. A greater oxygen supply in the littoral zone of the oligotrophic habitat at Bystock probably allowed certain of the aero-aquatic fungi, i.e, H. giganteum, H. triglitziense and C. zalewskii to compete more effectively against the established micro-flora of the decaying leaves, While an adequate supply of oxygen is probably the most important single factor which determines the frequency and distribution of these organisms in static water. other aspects of antagonistic microbial activity in decaying leaves may also play an important role in determining colonization patterns. These observations are supported by a comparison between colonization of sterile and non-sterile black disks in a laboratory experiment (Table 3) where it was shown that black sterile disks were more readily colonized than non-sterile ones when supplies of oxygen were similar. H. fractum colonized leached pine needles more effectively than beech leaves. This may explain
why this fungus is abundant at Bystock where pine needles form the greater part of the leaf litter. The absence of this species from Stoke Woods may be explained by its apparent inability to colonize black decaying leaves in competition with other micro-organisms andthe absence of suitable pine needle substrates there. This species has been recovered on numerous occasions from oligotrophic sites in Great Britain but appears to be absent from eutrophic habitats (Abdullah, Fisher & Webster, 1979). The colonization index (Cf) (Tables 2 and 3) represents the ratio colonized black disks : colonized brown disks and can give an indication of the saprophytic competitive ability of aero-aquatic hyphomycetes in a particular situation. Thus a high colonization index of 1'0 for H. giganteum and C. zalewskii at Bystock means equally effective colonization by the fungi of black and brown leaves, inferring high saprophytic competitive
Aero-aquatic Hyphomycetes
102
ability in that situation. Low colonization indices of 0 '4 and 0'06 for the same fungi at Stoke Woods suggest lower saprophytic competitive ability at the eutrophic site. In the field experiments freshly abscissed leaves were more readily colonized than decaying leaves. Yet when leaves are recovered from Stoke Woods black leaves are frequently colonized by aeroaquatic fungi while brown leaves are not. This may be explained by a time factor. Black leaves remain in the water from 8 months to 3 years while freshly abscissed leaves remain in the brown state for only 7-8 months. The time available for colonization of black leaves therefore exceeds that for brown leaves by four to five times. REFERENCES
P. J. & WEBSTER, J. (1979). Two new species of aero-aquatic hyphomycetes. Transactions of the British Mycological Society 72, 3 24--329.
ABDULLAH,
S. K.,
FISHER,
BARLOCHER, F . & KENDRICK, B. (1974). Dynamics of the
fungal population on leaves in a stream. Journal of Ecology 62, 761-791FISHER, P. J. (1977). New methods of detecting and studying saprophytic behaviour of aero-aquatic hyphomycetes from stagnant water. Transactions of the British Mycological Society 68, 407-411GLEN-BOTT, J. I. (1951). Helicodendron giganteum n.sp, and other aerial sporing hyphomycetes of submerged dead leaves. Transactions of the British Mycological Society 34, 275-279. GLEN-BOTT, J. I. (1955). On Helicodendron tubulosum and some similar species. Transactions of the British Mycological Society 38, 17-30. LINDER, D. H . (1929). A monograph of the helicosporous fungi imperfecti. Annals of the Missouri Botanical Gardens 16, 227-388. SANDERS, P. J. & ANDERSON, J. M. (1979). Colonization of wood blocks by aquatic hyphomycetes, Transactions of the British Mycological Society 73, 10310 7.
(Accepted for publication 8 November 1978)