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Periodicity of Cambium and the Formation of Xylem and Phloem in Mimusops elengi L., an Evergreen Member of Tropical India1)
Flora (1983) 173: 479-487
Periodicity of Cambium and the Formation of Xyl m and hlo m in Mimusops elengi L., an EV'erO'reen Member of Tropical Indial ) A. K. M.
GHOUSE
and
SHAMIMA HA HMI
D epartment of Botan y, A1igarh Muslim U ni vorsity, Aligarh , Indi a
Summary The periodioity of oambium and the forma tion of xylem and phloom h ave b o n studi d in Mimu80ps elengi L., for three consecutive calend a r y ear s (1974 to 1976) . It h as bo n fo und that following the thinning of the orown in April, n e w loaves em erge in May a n d t hi s is f ollow d by t he initiation of cambial aotivity in June, a fter a lapse of 4 weeks from the t ime of loaf m orgen o . Tho cambial activity continue s upto mid· November . X y lem f orma tion st arts from July and peocodos phloem formation which occurs from August to November .
Introduction Out of the many, only a few Indian tropical trees have so fa r been explored t o learn about their periodic activity of xylem and phloem production. The pioneering work of CHOWDHURY (1939, 1940, 1958) and CHOWDHURY & TAN DON (1950) on cambium periodicity still forms the only bulk of information on the subj ect . The other works include that of PALIWAL & PRASAD (1970) ; PALIWAL et al. (1975) and GHOUSE & HASHMI (1978, 1979a, 1979b, 1979c, 1980). It is, therefore, much r emains t o be done about this aspect of tree physiology in the Indian tropical tree flora. It is with this poin~ of view, the present work has b een undertaken to prov ido r elevant infor mation on the periodicity of cambium and the formation of xy lem a nd phloem in one of the many evergreen trees of India viz ., M i musops elengi L . ( S apotaceae).
Materials and Methods Cambial samples with some sapwood and seoonda r y phloem of M imu8o}J8 elengi L. , woro collected in the morning hours b etween 6 and 8 at for tnightly interva ls f or 3 oon sec ut ive calend ar y ears from 1974. On each turn, 3 trees were sample d a nd from eaoh t ree 4 blook s, each measuring 2.5 cm sq. were colleote d with the help of a chisel a nd h a mmer fr om the m a in trunks of 30 yoar old trees at chest h e ight ie . a bout 1.5 m from the gr ound level, one eaoh from the east, west, north and south side of the tree. The samples w er e fi xed on th e sp ot in FAA (Forma lin·acetic acid.alcohol), a spirate d after a n hour a nd preser ved in 70 % eth an ol af ter a week. Prior to sec· tioning, the samples were tre ated with a lco.glycerol mixture (equ al volumes of 50 % eth an ol and 50 % glycerol) for a period of 4- 6 week s to fecilitate sect ioning . All samples wore section ed on a sliding microtome at a thickness of 10- 12 [lm in tea n s ver se, r a di al and t a n gen t iall on g it uclinal 1) Dedicated to the m emory of Professor K . A. CHOWDHURY, the founde r of Plan t Anatomy
L aboratory in Aligarh Muslim Univers ity.
4 0
A . K . M. G no !om and S.
HAS liMI
pl n n<'". '1'1 1(' In ng<' nLill l Ro('t ion A paRs ing L1l1'oug h t ho cambi a l zono were s t a ine d with t a nni c acid n nd 1'(1I"' io (· Iol o,·id e fo ll o wing l<'osLo ,'s sc hodul o (F' os'r 1.934), Wll ile t h e r a dia l a nd tra n sverse ones \l Ne H[n in(1d inln (' m o id ('o m b inaL ion ( II Il AD L" ot a J. 1953 ). Aftor d ohy dra ting in e tha nol series, [h n "('('( io)\" \\ (' 1'(1 mo unLod ill llnad a ba lsa m . To HI IId ~ I ho pl w n o logy 0 (' t ho H Icotod t rees, 40 branc hos a t t he r ate of 10 p er side f acing IIH I , w<," I , lI od h a nd Ro u Lh W (1 " O Lagged wi t h a lumin iu m fe il s. W ee kly observa tions were m ade "('glt l'ding I ho I<'ltl' f,dl , n o w Ica f omO'l'gen r , ['l o w e ring a nd f r ui t ing h a bits of the sp ec ies unde r the I(wal on vi'·o ,ullo nl. T e n [I'oc" W ("'O s Ludi ed [ 0 " this purpose, during th e same p eriod of 3 calend ar )"'11 "" in "' hil'il [h o ('a m b ium pOl'i odi i ty has been st udied. Tho da l,t o n (, Iim.tl i" fac Lo .," UI;od in Lhi s s tud y w e re obta ined. from th e loca l m e teorolog ical lIlIi [ m n inl nill od It I [h o ni vO/'s i[ y a lnpus of Aligarh whi ch is gcogra phi cally loca t ed a t 27° 5 3' N InlL iLuci o .t nli 78° 4' I ~ I ng ilud o in Lh e ma nsoon b elt of t he Grea t Ga nge ti c Pla in of North India.
"n
Observations Th weel Iy obsorvations on phenology of the selected trees showed that the trees m a in t ain their vergr ee n h a bit at the local environment. However, there has been a c ns id l'a bl thinning of the foliage of the crown in April due to fall of old leaves, .f II wing th o l'i ;;o of t emper ature a nd the d eep d ecline in the relative humidity which t ucheH itR minimum in April in a calender year (Fig. 1). With the further rise of air t emp l'a tur in May, n ew leaves come up in large number to turn the dark crown of t h tr rs to a pa lo gr ee n one. The new leaf formation continues upto August and aft I' a short lapso during September, they emerge again in October and continue up to ovember (Fi g. 2). 700 , -----. -----.-----. ---__- .____~----~
J e-
F
11 e
0----" x······ .. ·x
A
t1
J
J
A
SON
D
REL. HU/1. % TO{PERATURE in °c RAIN FALL in em
Fig . 1. Graph .showing the monthly average of air temperature, r elative humidity and rain fall dUrin g the perIOd of the s tudy .
Periodicity of Ca mbium
4 1
[, : ~::jiiiiifi J
FHA
t1
J
~ LEAF FALL
IZZ1 LEAF Et1ERG. 1,:L;'l PRECUR . PHL.
J
A
§ _
SON.
D
CAN. ACTIVITY XYLEt1 PROD.
OIJ] PHL. PROD.
Fig. 2. Horizontal graphs sho w ing t he relationship b e tweon t h o p honolog ical {'ac to r'H lind th o tivity of vasc ula r camb ium a nd i ts vascular derivatives.
tI(· ·
The analysis of cambial samples collected at fortnightly intervals has revealed that the cambial initials undergo the first sign of reactivation in late May when some cells swell in radial direction and others under go various histochemical changcl'! (Fig. 3B) . The cells st a rt losing their coloure d contents and the nuclei become some· what hyaline. The vacuoles become prominent at this stage. The cambial cells undergo periclinal divisions as a following action, in the first week of June ie. after a lapse of at least 4 weeks from the time of emergence of n ew leaves. The weather at the local atmosphere becomes highly hot during this p eriod (Fig. 1) a nd, thus , it becomes ob· vious that a high air temperature is highly essential to initiate cell division in thc cambial initials of this evergreen sp ecies. The local weather b ecom es rough in late June or in early July when the mansoon· strikes the locality. After the mansoon showers, the a ir temperature goes down a little and the water content of the atmosphere rises to saturation or near saturation soo n. The locality experiences its major part of rain fall within the two month of July and August. In September , the rain fa ll slows down a nd in October, it becomcs sporadic. As a r esult of the above changes in the atmosph eric statu s, the relative humidity rises to its peak points in July- Augu st a nd shows a gradu a l decline in the following months (Fig. 1). Following cell division in cambial cells, the population of cambial zone swells up from July and touches its maximum in September to possess as many as 10- 12 layers of cells (Fig. 30). In October , the rate of cell division declines and it stops by mid· November. The cambium enter s its dorma nt phase in D ecember whence the dark contents in the initials reappear, particularly in ray initials (Fig. 3D) and the fusiform initials develop b eaded structure at radial walls. Thus the cambium of M. elengi remains active only for a period of 5 to 5.5 months in a calendar year. Prior to the reactivation of cambium in late Mayor in early June, a narrow strip of new phloem differentiates in early April, out of the outer derivatives which have formed at the end of the previous growth season. This precursor phloem measures about 75/-tm to I00!-lm in depth (Fig. 3A) . 32 Flora, Ed. 173
Fi g. :3. Ph otom ic rograph s s ho wing t he condit ion of vascu la r cambi um a nd the form ation of vascu la r c1 ori yati yo~. A , Apr il co ll oction show in g a p a rt of prec ursor phloem; B , May collec tion s h owin g t h swell ing of cambi a l in it ia l (arrow); C, S eptember collect ion showin g a wide zone of vasc ula ,· ca mb ium ; D , D eecmber collect ion sh owing the n ewly formed x y le m b elow the ca mbial zon nnc1 dorma!1t phlo m above . All a t X 372.
P eriodic ity of
amb ium
4 3
The current year xylem differentiates in July for thc firRt tim in a cal ndar y ar and this continues upto October. The xylem differentiation tak place wh n th relative humidity goes high , although the cambial population RtartR increafling from June, following the cell division in the initial. . After a month, from the tim of xyl m differentiation, the current year phloem formation commence. from AuguRt and this continues upto late November. The phloem differentiation , however, oceurR at a sl w rate from August to October and it attains it. peak in November. From AuguRt to October, this species produces about 500/.tm of phloem , while in ovemb l' alone the phloem differentiation amounts to about 1,200 flm. Tn all , .M . elengi produees 1,700 flm of phloem in a growth year and about 1,800 flm of phloem in a cal ndar year including the precursor type. The wood formation in thi species, on the oth r hand, amounts to about 2,000 /.tm in a growth year. Thus , almost an equal amount of xylem and phloem are produced by M. elengi with the initiation of xylem formation preceding that of phloem by a months period (Fig. 2).
Discussion Leaving aside a few tropical species, which grow throughout the year (ALVIM 1964 ; FAHN 1974), the majority of the hardwood species and conifers show a sharp periodic rhythm in their growth activity. The growth in tropical trees occurs for a longer period than in the temperate forms. Studies conducted by CHOWDHURY (1940, 1968, 1969) on cambial activity on some Indian tropical trees have revealed that the radial growth takes place as long as 10 months in a year. Similar studies of AMOS et al. (1950); FAHN & SARNAT (1963); WAISEL & FAHN (1965); WAISEL ct al. (1966); FAHN et al. (1968); LAWTON (1972); RAO (1972) and GHOUSE & HASHMI (1979a) have also shown that the cambium either remains active for a major part of a ycar or through out. The present study on M. elengi, has however, shown that this vergreen species behaves neither like a temperate tree nor like a true tropical one, as its cambium remains active only for a period of 5.5 months in a year. In all the three years of study, t he cambial reactivation has beenindicatcd by a slight expansion in size of the cambial initials in radial direction, a phenomcnon what has been described as swelling of the cambial zone by some earlier workcrs (CHOWDHURY 1969 ; PALIWAL & PRASAD 1970; PALIWAL et al. 1975 ; GUOUSE & HASHMI 1979a). This phenomenon has been noticed in the present study in late May ie., before the cell divisions actually initiated in the cambial zone and after 3 weekR from the time of new leaf emergence. The initiation of cambial activity in M. elengi after the emergence of new leaves clearly indicates its dependence on thc exten~ion growth, as in the case of other tropical and temperate trees studied earlier (COS'l'ER 1927/28; PRIESTLEY 1930 ; AVERY etal. 1937; CHOWDHUIW & TANDON 1950 ; WAREING 1956, 1958 ; CHOWDHURY 1958, 1969 ; WOR'r 1962 ; WAREING et al. 1964; W AISEL & F AHN 1965 ; W AISEL et al. 1966 ; F AHN et al. 1968 ; PALIWAL & PRASAD 1970 ; LAWTON 1972 ; GHOUSE & HASHMI 1979a). 32'
4
A . K. 1'. G 1l0UR F: fi nd
. Ff ASHM[
) n tlw pl'CS nt stud . , th i niti ati n of c 11 division in cam.bi al cells has been noticed OCC UI' in ,fUI1(' , fiS I' cO l'ded in so m ol't h 1 ndi an tr~~ s by CHOWDHURY (1968) with the ('x('('ptiOIl of Polyalthia lOl1gljo/in in which t ho initiation of cambial activity has been ob,,('i' cd It month ('arlior' th a ll in t hcrs i . in oarly May by GHOUSE & HASHMI ()979It) . TIl(' c('loll·mtion of ca mbial a tivity in 1If.. elengi h as been noticed to occur in mid - ()v('ml>c r in the) r so nt study . A Rimil al' Rituation of commencem ent of cambial acU ItLio n in ,Jun(' o,nd oR~o,t i on in mid- ov m.bor h aR been reported by the authors in It noth<'l' tl'opical 1,1'0 with deciduous ha bit v iz ., Delonix regin else wher e (1982). ')' Il(' (,It mbium turns dormant in lato Jo vO'm b or or in early D ecem.ber and remainR in t he "a mc statc' till n xt a l' wth RcaRo n Rtart, in June. 1 ~() II ()wi n g Lh \I divis io n .in tho cambial initials, a decrease in the d ensity of cell pl'oto pl M t a nd cc ll wa ll thiokening with a oon current reduction in size of beads on mdi tLi wa ll s a nd in the a mo un t of tanniferous substances in ray initials as noted in t h pl'osr nt invest igation h avo a lso beon reported by DERR & EVERT (1967) in Robinia 'P8etuloa acin, 'l'u KElt & EVER'J~ (1969) in Ace?' negundo , PALIWAL & PRASAD (1970) in J)alb ?'ght sissoo a nd GnOlJSE & H A lIMI (1979a) in Polynlthia longifolia .
Tho ca mbial d I'ivat ives diffore nti ate into xylem and phloem d ep ending on the at m Hphori c conditi o n . Xylom formation takes place when the r elative humidity go H hia h in Jul y a nd t he a ir tomporature com es down a little after rains. A similar w athol' fu,volll'ing xyl m formation has been noted in the case of Polyalthin longiJolia by 0 1( SE & HASliMI (1978). The initiation of phloem differentiation, on the otho l' hand, has b n notod in the present Rtudy in August during a growth year, a p l'i d of hot woathor undcr the local environment , although the w eather conditions ])t· va iling during Nov mber appears to be .h.ighly conducive for phloem differentiation, as in th' ea!:;c of l olyalthia longifolia (GUOUSE & HASHMI 1978) and D elonix regin ( 1I SE & H ASUM[ 1979 c). The present investigation further reveals that th e phloem di rr 1'0nt i ~tti n can occ ur in a comparatively high temperature , provided the internal conditions remain favourable fol' it. The pl'eCnrHOr phloem formation prior to the start of growth activity as found in tho ])1'01:\ nt inv stigation, ha also b ee n encounter ed in a number of cases investigated arliOl' both among the tcmperate as well as the tropical species (BROWN 1915 ; ABBE & HAWl'S 1939 ; AW£SOHWAGER 1950 ; WILOOX etal. 1956 ; GRILLOS & SMITH 1959 ; EVEHT 1960, 1963; SlUVASTAVA & O' BRIEN 1966 ; DERR & EVERT 1967; DAVIS & EVERT 1968 ; GHOUSE & HASHMI 1979b, 1979c, 1980) . Unlike in thc deciduous trees, M. elengi, b eing an evergreen species, shows the initia tion of xylem differentiation to preced e that of phloem (ART SCHWAGER 1945 ; FRASER 1952) and it continues to differentiate l at er as a simultaneous process along with phloem a in Carya illinoiensis (ARTSCUWAGER 1950) , Tilia americana (EVERT 1962) , Oelnstrus scandens (DAVIS & EVERT 1966) , Robinia pseudoacacia (DERR & EVEBT 1967) and Vitis riparia (DAVIS & EVERT 1970). In t he pre ently investigated sp ecies, the amount of phloem produced in a calnda r year happens to be only slightly lesser than that of xylem produced in a year.
Period ic iLy o f
lllnbi um
4 5
M. elengi is therefore not like thosc reported to produce 14- 15 times lnore 'Yl m than phloem in a calendar year (BANNA 1955 ; WIL 0 ]963) . It can be concluded from the prescnt study that thc cambial activity and thc rormation of vascular derivatives arc not only influ no d by the atmoRphcric weather conditions of the place in which the tree thrive, but al 0 arc influ need by a numb I' of physiological factors such as bud opening and new leaf em r g n . Th prcs nt investigation further indicates that a high temperature i e. Re nti al to initi at 11 division in the cambial initials and al. 0 for xylem differentiation but n t for ph.loem formation.
Acknowledgement The second a uthor (S. H.) expresses her g r ati t ude to tho Co un cil of SeionLific and lndllstri a1 Research, N ew D elhi, for the award of Post D octoral Fellowship.
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_
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(1968): Season a l d evelopm e nt of secondary phloem in Populus t,·emttloicles. Bot. Gaz. ) 29:
1- 8.
4
A. O K. M .
(j
!lO URE and S. H AS HM[
I)Eltlt, W. P., & !<;\' EIl1', H . /.'. ( 1967): T il e ra mbium and Robilli" jJHcw/ollcllcifl. n1(> I·. .J. 130t. 54:"/47 "/53.
~
asona L d vo lopment of tho p hl oem in
]<;Vlut1', Il . Ie. ( 1!J6()): l'IIlorm ,..l l·u(' tlll·o in Pynls commlln:i8 L. and its seas ona l ohangos. Un iv. eil lif. t'ubl. n ot. 32 : 127 194 . ( I !)(12): HOIH(' I1HP(,(·t" o f pil ioom dovo l prnont in rr i lia M1wl·icana. Am or. ,J. Bot. 49 : 659. ( I!HI:I): Tho ('n ,nilium lind HOHHo nll 1 d evc- lopnw nL 0 [' ph loom in PYI'US malus. Amor. J. Bot, 5 0 : 140 Illn, I,' li N, . (1074): !'Innt All ltlO lny . 1'('I'gnmon 1" '01'18, & :SAliN 'f" ,( I!lu:)): Xylom Htl'llr lu ,'o ftnd a rmu a L rh yt hm of deve Lopmont in troos and shrubs o f t 11 o d (,HIII't I V. HIII'lIb,... BII II . H('H. e un e. IH"ao l 11 : J!) 209. \ VAISAI" Y " & Ih :NJA MIN, L. (ID6): amb ial aot ivi ty in Acacie, r-addiana S av io Ann. Bot, 32 : 077 (HHi. 1"os'I',m, A. H. ( 1!):)4) : TII{\ li Ke o f Lnn 'l ic ac id a nd iL'on. c hloL'ide f or s t a ining m e r is t ematic tissues, iStnill 'I'(\(' ''no l. 9 : 0 1 H2. I,' ItM
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A. ( 1052): IniLiaLi on o f cambin l acL iv ity in so m o forest treos in Ontario. Ecology 33 :
27:1.
lI () t r;; I~,
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( I 070r): LOIl g'ov iLy of pll Lo m in D clOl~ix regie, RA~'IN. P1'oc. Ind ia n Aoad. S ci. (Plant-Sci.) 8 9 : u7 72. ( 1080): ,'ouHo na l p,.o d Llct io n of second a ry phl oem a nd its longevity in Mimusop s elengi L. ,·'Iom J7 0 : 175 170. (1.!l82): I mplteL of oxte ns ion g l'owth a nd fl o w o r ing on t he oambial ao tivi ty of Delonix re{fill [{Am, 1',.0('. Indi a n Acad. Sci. (J lant-Sci.) 91 : 201 - 209. >JtIl, IJOH, :So ,I ., & S~H'rll, I". 1-1.. (1959): Tho secondary p hloem of Douglas f ir. Forest Sc i, 5: 377 10 :)88. LAW1'ON, ,J , I{,. ( 1.1)7 2): ROHHona l vU l'i at io n in th e sooonda ry phlocm of som e forest trees from NigO l'in II , SL I'l,(:Lul'o of t ho ph loe m. Now I'I 'ytol. 71 : 335- ~48.
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R AO,
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NOAH, I., & FAliN, A. (1966): Camb ia l activ ity in Eucalyp tus camaldulensis D eh n. I. The r olation 1,0 oxtons ion growth in young sap ling. L a-Yaaran 16 : 103- 108.
VVA.REI 0, 1'. F , ( 1956): P h otope ri od ism in woody p l ants. Ann. R ev. P lant Phys iol. 7 : 191- 214, (195 ): Th o physiology of cambi a l ac t ivity. J. Inst. Wood. Sc i. 1 : 34- 42.
I'e l'iodicity o f
nmbi um
4 7
HANNEY, C. E. A., & l)W BY, .r. ( 1964): Tho r o lo of ondog0nO~1" hO"m o n (,H in ('Ilmh i,ll <1('1 il' il Y and xyl om d iffeL'onti at ion. In: T ho fcmnnt ion of \\'oo d in fO"('~ 1 tn'PH (N\. ~ \. I\\. Z'MM E H'lAN) . Acad om ic 1" 'ess, Now Y ork (pp. 323 344). WILCOX, H., CZABATOl{, F. ,J., G 'BOLAMI, G., l\'TOBI"LAN Il , D. E., C' fi~lITIi. H. F. (10:;(\): h('m i('.d deb a rking of s omo pu lp \I'ood tI'OO~, 'I'oc h. Pub!. 77 ::-llnle llnil·. . LT. Co l!. o f 1"OI'(·HI,'.I, WILSON, B. F, (1963): Incroaso in coli wa ll KUl'fare fil'(\11 dU "ing (,Illal'gpm n n l of t'nmh ill l (\til' iI',t! il'PH in Abies concolor . Amor . ,J. Bot, 50 : 95- 102. WOHT, D, .J , (1962): Ph Y' io logy of cambi a l ne l i\'i t y, In: T ,'('(' G ,'o \\'1 h ('d, T, 'I'. KO ZL() \\ ~ '{I). Ron a ld P ,'oss, N o w York (pp, 89 95) . R ecei ved M a rc h 3, 1982 Auth ors ' addressos: Dr, A. K . M . GHO lISE, '1" '03 G ro wth and EIlI' il'onmonL 1: (,HOIl I'(' h L nho l'ator ies, Department of Botany, A li ga l'h Mu s l im Univ(, I'Hi ty, A lig'lI'h 20200 1, I ndia; Dr, P l iHH} SHAMIMA HASHMI, S. R. 0., P harmocognosy L a b. , Dc pa l'tmrnt of B tn n y, Aligl\l'h 1\111 Hlim LT niver s ity, Aligar h 202001, Ind ia.
Periodicity of Cambium and the Formation of Xyl m and hlo m in Mimusops elengi L., an EV'erO'reen Member of Tropical Indial ) A. K. M.
GHOUSE
and
SHAMIMA HA HMI
D epartment of Botan y, A1igarh Muslim U ni vorsity, Aligarh , Indi a
Summary The periodioity of oambium and the forma tion of xylem and phloom h ave b o n studi d in Mimu80ps elengi L., for three consecutive calend a r y ear s (1974 to 1976) . It h as bo n fo und that following the thinning of the orown in April, n e w loaves em erge in May a n d t hi s is f ollow d by t he initiation of cambial aotivity in June, a fter a lapse of 4 weeks from the t ime of loaf m orgen o . Tho cambial activity continue s upto mid· November . X y lem f orma tion st arts from July and peocodos phloem formation which occurs from August to November .
Introduction Out of the many, only a few Indian tropical trees have so fa r been explored t o learn about their periodic activity of xylem and phloem production. The pioneering work of CHOWDHURY (1939, 1940, 1958) and CHOWDHURY & TAN DON (1950) on cambium periodicity still forms the only bulk of information on the subj ect . The other works include that of PALIWAL & PRASAD (1970) ; PALIWAL et al. (1975) and GHOUSE & HASHMI (1978, 1979a, 1979b, 1979c, 1980). It is, therefore, much r emains t o be done about this aspect of tree physiology in the Indian tropical tree flora. It is with this poin~ of view, the present work has b een undertaken to prov ido r elevant infor mation on the periodicity of cambium and the formation of xy lem a nd phloem in one of the many evergreen trees of India viz ., M i musops elengi L . ( S apotaceae).
Materials and Methods Cambial samples with some sapwood and seoonda r y phloem of M imu8o}J8 elengi L. , woro collected in the morning hours b etween 6 and 8 at for tnightly interva ls f or 3 oon sec ut ive calend ar y ears from 1974. On each turn, 3 trees were sample d a nd from eaoh t ree 4 blook s, each measuring 2.5 cm sq. were colleote d with the help of a chisel a nd h a mmer fr om the m a in trunks of 30 yoar old trees at chest h e ight ie . a bout 1.5 m from the gr ound level, one eaoh from the east, west, north and south side of the tree. The samples w er e fi xed on th e sp ot in FAA (Forma lin·acetic acid.alcohol), a spirate d after a n hour a nd preser ved in 70 % eth an ol af ter a week. Prior to sec· tioning, the samples were tre ated with a lco.glycerol mixture (equ al volumes of 50 % eth an ol and 50 % glycerol) for a period of 4- 6 week s to fecilitate sect ioning . All samples wore section ed on a sliding microtome at a thickness of 10- 12 [lm in tea n s ver se, r a di al and t a n gen t iall on g it uclinal 1) Dedicated to the m emory of Professor K . A. CHOWDHURY, the founde r of Plan t Anatomy
L aboratory in Aligarh Muslim Univers ity.
4 0
A . K . M. G no !om and S.
HAS liMI
pl n n<'". '1'1 1(' In ng<' nLill l Ro('t ion A paRs ing L1l1'oug h t ho cambi a l zono were s t a ine d with t a nni c acid n nd 1'(1I"' io (· Iol o,·id e fo ll o wing l<'osLo ,'s sc hodul o (F' os'r 1.934), Wll ile t h e r a dia l a nd tra n sverse ones \l Ne H[n in(1d inln (' m o id ('o m b inaL ion ( II Il AD L" ot a J. 1953 ). Aftor d ohy dra ting in e tha nol series, [h n "('('( io)\" \\ (' 1'(1 mo unLod ill llnad a ba lsa m . To HI IId ~ I ho pl w n o logy 0 (' t ho H Icotod t rees, 40 branc hos a t t he r ate of 10 p er side f acing IIH I , w<," I , lI od h a nd Ro u Lh W (1 " O Lagged wi t h a lumin iu m fe il s. W ee kly observa tions were m ade "('glt l'ding I ho I<'ltl' f,dl , n o w Ica f omO'l'gen r , ['l o w e ring a nd f r ui t ing h a bits of the sp ec ies unde r the I(wal on vi'·o ,ullo nl. T e n [I'oc" W ("'O s Ludi ed [ 0 " this purpose, during th e same p eriod of 3 calend ar )"'11 "" in "' hil'il [h o ('a m b ium pOl'i odi i ty has been st udied. Tho da l,t o n (, Iim.tl i" fac Lo .," UI;od in Lhi s s tud y w e re obta ined. from th e loca l m e teorolog ical lIlIi [ m n inl nill od It I [h o ni vO/'s i[ y a lnpus of Aligarh whi ch is gcogra phi cally loca t ed a t 27° 5 3' N InlL iLuci o .t nli 78° 4' I ~ I ng ilud o in Lh e ma nsoon b elt of t he Grea t Ga nge ti c Pla in of North India.
"n
Observations Th weel Iy obsorvations on phenology of the selected trees showed that the trees m a in t ain their vergr ee n h a bit at the local environment. However, there has been a c ns id l'a bl thinning of the foliage of the crown in April due to fall of old leaves, .f II wing th o l'i ;;o of t emper ature a nd the d eep d ecline in the relative humidity which t ucheH itR minimum in April in a calender year (Fig. 1). With the further rise of air t emp l'a tur in May, n ew leaves come up in large number to turn the dark crown of t h tr rs to a pa lo gr ee n one. The new leaf formation continues upto August and aft I' a short lapso during September, they emerge again in October and continue up to ovember (Fi g. 2). 700 , -----. -----.-----. ---__- .____~----~
J e-
F
11 e
0----" x······ .. ·x
A
t1
J
J
A
SON
D
REL. HU/1. % TO{PERATURE in °c RAIN FALL in em
Fig . 1. Graph .showing the monthly average of air temperature, r elative humidity and rain fall dUrin g the perIOd of the s tudy .
Periodicity of Ca mbium
4 1
[, : ~::jiiiiifi J
FHA
t1
J
~ LEAF FALL
IZZ1 LEAF Et1ERG. 1,:L;'l PRECUR . PHL.
J
A
§ _
SON.
D
CAN. ACTIVITY XYLEt1 PROD.
OIJ] PHL. PROD.
Fig. 2. Horizontal graphs sho w ing t he relationship b e tweon t h o p honolog ical {'ac to r'H lind th o tivity of vasc ula r camb ium a nd i ts vascular derivatives.
tI(· ·
The analysis of cambial samples collected at fortnightly intervals has revealed that the cambial initials undergo the first sign of reactivation in late May when some cells swell in radial direction and others under go various histochemical changcl'! (Fig. 3B) . The cells st a rt losing their coloure d contents and the nuclei become some· what hyaline. The vacuoles become prominent at this stage. The cambial cells undergo periclinal divisions as a following action, in the first week of June ie. after a lapse of at least 4 weeks from the time of emergence of n ew leaves. The weather at the local atmosphere becomes highly hot during this p eriod (Fig. 1) a nd, thus , it becomes ob· vious that a high air temperature is highly essential to initiate cell division in thc cambial initials of this evergreen sp ecies. The local weather b ecom es rough in late June or in early July when the mansoon· strikes the locality. After the mansoon showers, the a ir temperature goes down a little and the water content of the atmosphere rises to saturation or near saturation soo n. The locality experiences its major part of rain fall within the two month of July and August. In September , the rain fa ll slows down a nd in October, it becomcs sporadic. As a r esult of the above changes in the atmosph eric statu s, the relative humidity rises to its peak points in July- Augu st a nd shows a gradu a l decline in the following months (Fig. 1). Following cell division in cambial cells, the population of cambial zone swells up from July and touches its maximum in September to possess as many as 10- 12 layers of cells (Fig. 30). In October , the rate of cell division declines and it stops by mid· November. The cambium enter s its dorma nt phase in D ecember whence the dark contents in the initials reappear, particularly in ray initials (Fig. 3D) and the fusiform initials develop b eaded structure at radial walls. Thus the cambium of M. elengi remains active only for a period of 5 to 5.5 months in a calendar year. Prior to the reactivation of cambium in late Mayor in early June, a narrow strip of new phloem differentiates in early April, out of the outer derivatives which have formed at the end of the previous growth season. This precursor phloem measures about 75/-tm to I00!-lm in depth (Fig. 3A) . 32 Flora, Ed. 173
Fi g. :3. Ph otom ic rograph s s ho wing t he condit ion of vascu la r cambi um a nd the form ation of vascu la r c1 ori yati yo~. A , Apr il co ll oction show in g a p a rt of prec ursor phloem; B , May collec tion s h owin g t h swell ing of cambi a l in it ia l (arrow); C, S eptember collect ion showin g a wide zone of vasc ula ,· ca mb ium ; D , D eecmber collect ion sh owing the n ewly formed x y le m b elow the ca mbial zon nnc1 dorma!1t phlo m above . All a t X 372.
P eriodic ity of
amb ium
4 3
The current year xylem differentiates in July for thc firRt tim in a cal ndar y ar and this continues upto October. The xylem differentiation tak place wh n th relative humidity goes high , although the cambial population RtartR increafling from June, following the cell division in the initial. . After a month, from the tim of xyl m differentiation, the current year phloem formation commence. from AuguRt and this continues upto late November. The phloem differentiation , however, oceurR at a sl w rate from August to October and it attains it. peak in November. From AuguRt to October, this species produces about 500/.tm of phloem , while in ovemb l' alone the phloem differentiation amounts to about 1,200 flm. Tn all , .M . elengi produees 1,700 flm of phloem in a growth year and about 1,800 flm of phloem in a cal ndar year including the precursor type. The wood formation in thi species, on the oth r hand, amounts to about 2,000 /.tm in a growth year. Thus , almost an equal amount of xylem and phloem are produced by M. elengi with the initiation of xylem formation preceding that of phloem by a months period (Fig. 2).
Discussion Leaving aside a few tropical species, which grow throughout the year (ALVIM 1964 ; FAHN 1974), the majority of the hardwood species and conifers show a sharp periodic rhythm in their growth activity. The growth in tropical trees occurs for a longer period than in the temperate forms. Studies conducted by CHOWDHURY (1940, 1968, 1969) on cambial activity on some Indian tropical trees have revealed that the radial growth takes place as long as 10 months in a year. Similar studies of AMOS et al. (1950); FAHN & SARNAT (1963); WAISEL & FAHN (1965); WAISEL ct al. (1966); FAHN et al. (1968); LAWTON (1972); RAO (1972) and GHOUSE & HASHMI (1979a) have also shown that the cambium either remains active for a major part of a ycar or through out. The present study on M. elengi, has however, shown that this vergreen species behaves neither like a temperate tree nor like a true tropical one, as its cambium remains active only for a period of 5.5 months in a year. In all the three years of study, t he cambial reactivation has beenindicatcd by a slight expansion in size of the cambial initials in radial direction, a phenomcnon what has been described as swelling of the cambial zone by some earlier workcrs (CHOWDHURY 1969 ; PALIWAL & PRASAD 1970; PALIWAL et al. 1975 ; GUOUSE & HASHMI 1979a). This phenomenon has been noticed in the present study in late May ie., before the cell divisions actually initiated in the cambial zone and after 3 weekR from the time of new leaf emergence. The initiation of cambial activity in M. elengi after the emergence of new leaves clearly indicates its dependence on thc exten~ion growth, as in the case of other tropical and temperate trees studied earlier (COS'l'ER 1927/28; PRIESTLEY 1930 ; AVERY etal. 1937; CHOWDHUIW & TANDON 1950 ; WAREING 1956, 1958 ; CHOWDHURY 1958, 1969 ; WOR'r 1962 ; WAREING et al. 1964; W AISEL & F AHN 1965 ; W AISEL et al. 1966 ; F AHN et al. 1968 ; PALIWAL & PRASAD 1970 ; LAWTON 1972 ; GHOUSE & HASHMI 1979a). 32'
4
A . K. 1'. G 1l0UR F: fi nd
. Ff ASHM[
) n tlw pl'CS nt stud . , th i niti ati n of c 11 division in cam.bi al cells has been noticed OCC UI' in ,fUI1(' , fiS I' cO l'ded in so m ol't h 1 ndi an tr~~ s by CHOWDHURY (1968) with the ('x('('ptiOIl of Polyalthia lOl1gljo/in in which t ho initiation of cambial activity has been ob,,('i' cd It month ('arlior' th a ll in t hcrs i . in oarly May by GHOUSE & HASHMI ()979It) . TIl(' c('loll·mtion of ca mbial a tivity in 1If.. elengi h as been noticed to occur in mid - ()v('ml>c r in the) r so nt study . A Rimil al' Rituation of commencem ent of cambial acU ItLio n in ,Jun(' o,nd oR~o,t i on in mid- ov m.bor h aR been reported by the authors in It noth<'l' tl'opical 1,1'0 with deciduous ha bit v iz ., Delonix regin else wher e (1982). ')' Il(' (,It mbium turns dormant in lato Jo vO'm b or or in early D ecem.ber and remainR in t he "a mc statc' till n xt a l' wth RcaRo n Rtart, in June. 1 ~() II ()wi n g Lh \I divis io n .in tho cambial initials, a decrease in the d ensity of cell pl'oto pl M t a nd cc ll wa ll thiokening with a oon current reduction in size of beads on mdi tLi wa ll s a nd in the a mo un t of tanniferous substances in ray initials as noted in t h pl'osr nt invest igation h avo a lso beon reported by DERR & EVERT (1967) in Robinia 'P8etuloa acin, 'l'u KElt & EVER'J~ (1969) in Ace?' negundo , PALIWAL & PRASAD (1970) in J)alb ?'ght sissoo a nd GnOlJSE & H A lIMI (1979a) in Polynlthia longifolia .
Tho ca mbial d I'ivat ives diffore nti ate into xylem and phloem d ep ending on the at m Hphori c conditi o n . Xylom formation takes place when the r elative humidity go H hia h in Jul y a nd t he a ir tomporature com es down a little after rains. A similar w athol' fu,volll'ing xyl m formation has been noted in the case of Polyalthin longiJolia by 0 1( SE & HASliMI (1978). The initiation of phloem differentiation, on the otho l' hand, has b n notod in the present Rtudy in August during a growth year, a p l'i d of hot woathor undcr the local environment , although the w eather conditions ])t· va iling during Nov mber appears to be .h.ighly conducive for phloem differentiation, as in th' ea!:;c of l olyalthia longifolia (GUOUSE & HASHMI 1978) and D elonix regin ( 1I SE & H ASUM[ 1979 c). The present investigation further reveals that th e phloem di rr 1'0nt i ~tti n can occ ur in a comparatively high temperature , provided the internal conditions remain favourable fol' it. The pl'eCnrHOr phloem formation prior to the start of growth activity as found in tho ])1'01:\ nt inv stigation, ha also b ee n encounter ed in a number of cases investigated arliOl' both among the tcmperate as well as the tropical species (BROWN 1915 ; ABBE & HAWl'S 1939 ; AW£SOHWAGER 1950 ; WILOOX etal. 1956 ; GRILLOS & SMITH 1959 ; EVEHT 1960, 1963; SlUVASTAVA & O' BRIEN 1966 ; DERR & EVERT 1967; DAVIS & EVERT 1968 ; GHOUSE & HASHMI 1979b, 1979c, 1980) . Unlike in thc deciduous trees, M. elengi, b eing an evergreen species, shows the initia tion of xylem differentiation to preced e that of phloem (ART SCHWAGER 1945 ; FRASER 1952) and it continues to differentiate l at er as a simultaneous process along with phloem a in Carya illinoiensis (ARTSCUWAGER 1950) , Tilia americana (EVERT 1962) , Oelnstrus scandens (DAVIS & EVERT 1966) , Robinia pseudoacacia (DERR & EVEBT 1967) and Vitis riparia (DAVIS & EVERT 1970). In t he pre ently investigated sp ecies, the amount of phloem produced in a calnda r year happens to be only slightly lesser than that of xylem produced in a year.
Period ic iLy o f
lllnbi um
4 5
M. elengi is therefore not like thosc reported to produce 14- 15 times lnore 'Yl m than phloem in a calendar year (BANNA 1955 ; WIL 0 ]963) . It can be concluded from the prescnt study that thc cambial activity and thc rormation of vascular derivatives arc not only influ no d by the atmoRphcric weather conditions of the place in which the tree thrive, but al 0 arc influ need by a numb I' of physiological factors such as bud opening and new leaf em r g n . Th prcs nt investigation further indicates that a high temperature i e. Re nti al to initi at 11 division in the cambial initials and al. 0 for xylem differentiation but n t for ph.loem formation.
Acknowledgement The second a uthor (S. H.) expresses her g r ati t ude to tho Co un cil of SeionLific and lndllstri a1 Research, N ew D elhi, for the award of Post D octoral Fellowship.
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_
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4
A. O K. M .
(j
!lO URE and S. H AS HM[
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~
asona L d vo lopment of tho p hl oem in
]<;Vlut1', Il . Ie. ( 1!J6()): l'IIlorm ,..l l·u(' tlll·o in Pynls commlln:i8 L. and its seas ona l ohangos. Un iv. eil lif. t'ubl. n ot. 32 : 127 194 . ( I !)(12): HOIH(' I1HP(,(·t" o f pil ioom dovo l prnont in rr i lia M1wl·icana. Am or. ,J. Bot. 49 : 659. ( I!HI:I): Tho ('n ,nilium lind HOHHo nll 1 d evc- lopnw nL 0 [' ph loom in PYI'US malus. Amor. J. Bot, 5 0 : 140 Illn, I,' li N, . (1074): !'Innt All ltlO lny . 1'('I'gnmon 1" '01'18, & :SAliN 'f" ,( I!lu:)): Xylom Htl'llr lu ,'o ftnd a rmu a L rh yt hm of deve Lopmont in troos and shrubs o f t 11 o d (,HIII't I V. HIII'lIb,... BII II . H('H. e un e. IH"ao l 11 : J!) 209. \ VAISAI" Y " & Ih :NJA MIN, L. (ID6): amb ial aot ivi ty in Acacie, r-addiana S av io Ann. Bot, 32 : 077 (HHi. 1"os'I',m, A. H. ( 1!):)4) : TII{\ li Ke o f Lnn 'l ic ac id a nd iL'on. c hloL'ide f or s t a ining m e r is t ematic tissues, iStnill 'I'(\(' ''no l. 9 : 0 1 H2. I,' ItM
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27:1.
lI () t r;; I~,
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( I 070r): LOIl g'ov iLy of pll Lo m in D clOl~ix regie, RA~'IN. P1'oc. Ind ia n Aoad. S ci. (Plant-Sci.) 8 9 : u7 72. ( 1080): ,'ouHo na l p,.o d Llct io n of second a ry phl oem a nd its longevity in Mimusop s elengi L. ,·'Iom J7 0 : 175 170. (1.!l82): I mplteL of oxte ns ion g l'owth a nd fl o w o r ing on t he oambial ao tivi ty of Delonix re{fill [{Am, 1',.0('. Indi a n Acad. Sci. (J lant-Sci.) 91 : 201 - 209. >JtIl, IJOH, :So ,I ., & S~H'rll, I". 1-1.. (1959): Tho secondary p hloem of Douglas f ir. Forest Sc i, 5: 377 10 :)88. LAW1'ON, ,J , I{,. ( 1.1)7 2): ROHHona l vU l'i at io n in th e sooonda ry phlocm of som e forest trees from NigO l'in II , SL I'l,(:Lul'o of t ho ph loe m. Now I'I 'ytol. 71 : 335- ~48.
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R AO,
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' VAL, E L , Y ., & FAll , A . (1965): The e ffeo ts of environment on t he wood format ion and camb ial act ivity in Robinia, pseucloacacia. N e w P hyto l. 64 : 436- 442. -
NOAH, I., & FAliN, A. (1966): Camb ia l activ ity in Eucalyp tus camaldulensis D eh n. I. The r olation 1,0 oxtons ion growth in young sap ling. L a-Yaaran 16 : 103- 108.
VVA.REI 0, 1'. F , ( 1956): P h otope ri od ism in woody p l ants. Ann. R ev. P lant Phys iol. 7 : 191- 214, (195 ): Th o physiology of cambi a l ac t ivity. J. Inst. Wood. Sc i. 1 : 34- 42.
I'e l'iodicity o f
nmbi um
4 7
HANNEY, C. E. A., & l)W BY, .r. ( 1964): Tho r o lo of ondog0nO~1" hO"m o n (,H in ('Ilmh i,ll <1('1 il' il Y and xyl om d iffeL'onti at ion. In: T ho fcmnnt ion of \\'oo d in fO"('~ 1 tn'PH (N\. ~ \. I\\. Z'MM E H'lAN) . Acad om ic 1" 'ess, Now Y ork (pp. 323 344). WILCOX, H., CZABATOl{, F. ,J., G 'BOLAMI, G., l\'TOBI"LAN Il , D. E., C' fi~lITIi. H. F. (10:;(\): h('m i('.d deb a rking of s omo pu lp \I'ood tI'OO~, 'I'oc h. Pub!. 77 ::-llnle llnil·. . LT. Co l!. o f 1"OI'(·HI,'.I, WILSON, B. F, (1963): Incroaso in coli wa ll KUl'fare fil'(\11 dU "ing (,Illal'gpm n n l of t'nmh ill l (\til' iI',t! il'PH in Abies concolor . Amor . ,J. Bot, 50 : 95- 102. WOHT, D, .J , (1962): Ph Y' io logy of cambi a l ne l i\'i t y, In: T ,'('(' G ,'o \\'1 h ('d, T, 'I'. KO ZL() \\ ~ '{I). Ron a ld P ,'oss, N o w York (pp, 89 95) . R ecei ved M a rc h 3, 1982 Auth ors ' addressos: Dr, A. K . M . GHO lISE, '1" '03 G ro wth and EIlI' il'onmonL 1: (,HOIl I'(' h L nho l'ator ies, Department of Botany, A li ga l'h Mu s l im Univ(, I'Hi ty, A lig'lI'h 20200 1, I ndia; Dr, P l iHH} SHAMIMA HASHMI, S. R. 0., P harmocognosy L a b. , Dc pa l'tmrnt of B tn n y, Aligl\l'h 1\111 Hlim LT niver s ity, Aligar h 202001, Ind ia.