A Further Contribution to the Endosperm of the Cucurbitaceae 401

A FURTHER CONTRIBUTION TO THE ENDOSPERIM OF THE CUCURBITACEAE

BY DALBIR SINGH (Departraent of Botany, University of Ralasthan, Jaipur) Rex~ived August 4, 1964 (Commtmicatcd by Dr. C. V. Subramanian, r.A.tC.)

INTRODUCTION THE previous literature on the endosperm of the Cucurbitaceac has already been reviewed (Singh, 1957). Since then Chopra and Agrawal (1958) have described the structure and development of the chalazal endosperm haustorium in Benincasa cerifera Sa~;i., Cucumis melo vat. utilissimus Roxb., Luffa cylindrica (L.) Roem. (syn. L. aegyptiaca Mill.), and Melothria heterophylla Cogn. The variations in structure, size and form of the haustorium arc remarkable in this family. The present paper deals with a comparative account of endosperm development, structure of the chalazal endosperm haustorium and the behaviour of endosperm nuclei during advanced stages of its development in fifteen members of the Cucurbitaceae.

MATERIALS AND METHODS The material was collected from a number of localities in Northern India (Table I). Formalin acetic alcohol was used for fixation; and the usual methods of dehydration, embedding, sectioning and staining were followed. The endsoperm was also dissected out, stained with acetocalmine and mounted in glycerine jelly. To study the nuclear changes, cellular endopselm was smeared and stained with acetocarmine.

OBSERVATIONS The ovule is anatropous, bitegmic and crassinueellate in all the plants. It is erect in Cyclanthera; pendulous in Actinostemma, Dicoelospermum, Edgaria and Herpetospermum; and horizontal or slightly obliquely disposed in the remaining plants.. Development of endosperm.--The embryo-sac enlarges after fertilization (Fig. 41). This is more pronounced in Actinostemma, Cucumis, Cyclanthera, 399 40O DALBIR SINGH

ThnL~ I Locality and time of collection of the investigated plants

Name of plant Collected by Locality Time

Aetinostemma tenerum Griff. M. R. Sharma Hastinapur Sept. 1962 (Meerut) Citrullus lanatus (Thunb.) Mansf. Author Jodhpur Sept. 1961 Corallocarpus conocarpus (Dalz. and do. do. do. Gibs.) Clarke C. epigaeus (Rottl. and Willd.) Clarke do. do. do. Cueumis prophetarum Linn. do. do. do. C. melo var. momordica Roxb. do. do. do. Cyclanthera pedata Sehrad. do. Darjeeling Oct. 1954 Dactyliandra welwitschiiHook. f. do. Jodhpur Sept. 1962 Dicoelospermum ritchiei Clarke S.N. Chaturv~li Paehmari Oct. 1956 Edgaria darjeelingensis Clarke Author Darjeeling Oct. 1954 Herpetospermum pedun¢ulosum (Ser.) do. do. do. Clarke* Luffa echinata Roxb. R. M. Bhandari Bharatpur Oct. 1961 L. graveolens Roxb. Author Mala forest Oct. 1956 (Pilibhit) L. hermaphrodita Singh and Bhandari** do. Agra Aug. 1954 Trichsanthes cucumerina Linn. do. Katihar Oct. 1954 (Bihar)

* This plant was misidenfified as Thladiantha calcarata earlier (see Sing/a, 1957). ** Luffa hermaphrodita, a new species from India (Singh and Bhandari, 1963).

Dieoelospermum, Edgaria, Herpetospermum and Trichosanthes (Figs. 26, 38) and less so in Citrullus, Corallocarpus, Dactyliandra and Luffa (Figs. 1, 48, 50). Simultaneously, the primary endosperm nucleus, after repeated divisions, produces a large number of free nuclei which form a lining layer at the periphery of the embryo-sac. The upper part of the embryo-sac dilates (Figs. 5, 26, 42, 48) and the lower remains as a narrow and tubular caecum in all the plants except Corallocarpus conocarpus. In C. conocarpus a tubular caecum is never differentiated but the chalazal end o:f the embryo-sac is taper- ing during earlier stages (Figs. 1, 2). Finally, it becomes broad (Figs. 3, 4) ; chalazal endosperm haustorium is, therefore, absent in C. conocarpus. In A Further Contribution to the Endosperm of the Cucurbitaceae 401

the remaining plants the upper dilated part of the embryo-sac develops the endosperm proper and the chalazal tubular caecum functions as a haustorium which penefrates the nucelius. Wall formation initiates in the dilated part of the embryo-sac after the proembryo reaches the globular stage. Starting close to the embryo, it extends centripetally downwards. The endosperm proper becomes completely cellular in all plants except C. melo var. momordica, E. darjeelingensis and H. pedunculosum in which a free nuclear portion is left in the endosperm above the narrow caecum (Figs. 27, 43, 44, 45). Rarely, a similar coenocytic portion of endosperm may also persist in D. welwitschii and D. ritchiei (Fig. 35). The chalazal endosperm haustorium in these plants, therefore, possesses a bulbous free nuclear base at the junction with endosperm proper. In Citrullus lanatus and Coratloearpus epigaeus, the wall formation may extend into the chalazal endosperm haustorium making it cellular (Figs. 8, 10, 14, 16). The wall formation in a haustorium is also progressive ; in one case, however, a transverse wall was laid down in the chalazal endosperm caecum in C. epigaeus even before the wall formation could initiate in its vesicular part (Fig. 5). The chalazal endosperm haustorium assumes its shape after the Wali formation is complete in the dilated part of the embryo-sac. Its appearance varies in different species and rarely in the same species also. A haustorium is absent in Corallocarpus conocarpus (Fig. 4), but it is short and Farlty or completely cellular in C. epigaeus (Figs. 6-I0). Rarely it may also remain coenocytic in C. epigaeus. The haustorium is coenocytic as well as celk:lar in Citrullus lanatus in an approximate ratio of 3:7 (Figs. 11-21). The cells of the cellular haustorium undergo divisions fo~ming a massive structure (Figs. 18, 19). The haustorium remains coenccytic in the remaining pt,~nts (Figs. 24, 27, 30, 34, 37, 39, z[4, 45, 46, 49, 51, 52); occasionally a few cells are formed in its proximal part in Cucumis prophetarum (Figs. 31, 32). The size of the haustorium is variable in different species (see Table II) and it does not bear any relation to the size of the ovule and endospelm proFer. Table II provides the length and breadth (L × B) of the chalazal c ndosperm haustorium, ovule and endosFeIm proper at the globular stage of the embryo, in the investigated species. The tip of the haustorium is usually narrow and rounded but in A. tenerum, C. epigaeus and C. melo var. mcmordica it is not so. It is globular or cylil~dri- caI, and entire or lobed in A. tenerum (Figs. 22-25); acute, broad and dub- shaped in C. ep{gaeus (Figs. 9, 10); and aristate, truncate ~nd dub-shaped 402 DA~m S~NGI-I

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TABLE II

Size of ovule, endosperm proper and its haustorium in the investigated species

Endosperm Ovulo proper Haustorium Nature Name of plant L x B L x B L x B of ill ram, in microm in microns haustodum

Acttnostemma tenerum 8X 5 2,000x 160 6,200-7,100 × 40-200 Coenoeytt¢ Citrullus lanatus 5x 3 600- 440x 440- 640× 60 Cellular or 500- 320 coenoeytl¢

Coralloearpus conoearpus 5 x 3 440 x 300 el Absent C. epigaeus 4" 5 x 3 500 x 400 360-- 440x 40- 80 Partly or wholly cellular Cucumis prophetarum 5" 5 x 3 600× 360 900-1,500x 40- 60 Coenoeytic C. melo var. momordica 7 x 3"5 400× 320 2,300x 30- 40 y~ Cyclanthera pedata I0 x 7 1,800 1,400 8,900 x 80-120 lP

2)actyliandra weIwitst~hii 6 × 3 300 200 840 x 80-120 lP Dieoelospermum ritchiei 3.5 × 2.5 1,800× 600 3,200x 40- 80 Jl Edgaria darjeelingensis 12 x 7 1,200x 900 3,200x 100-120 P~ Herpetospermum pedun- 15 × 13 1,500x 1,200 2,700 x 60-100 PI culosurn Luffa echinata 6 x 4 400 x 300 240- 450× 40- 60 ,, L. graveolens 5" 5 × 4 480x 300 900 × 40- 60 ,, L. hermaphrodita 6 × 4 400 × 300 700- 900x 40- 60 ,, Trichosanthes eucumerina 10 x 8 1,600x 1,400 3,800-4,700x 40- 60 ,,

in C. me[o var. momordica (Figs. 27, 28, 29). Usually the haustorium occupies a median position at the base of the cellular endosperm. In Citrullus lanatus and Corallocarpus epigaeus, however, due to asymmetrical growth of the cellular endosperm, the haustorium is usually pushed to a more or less lateral position (Figs. 7, 9, 17, 18).

The coenocytic haustorium remains active till the embryo attains the heart-shaped stage. Later on, however, its activity declines, it loses contents, and the developing endosperm presses on the flaccid haustorium which even- tually coils. The coiled, empty and loose haustorium persists for some time with the endosperm proper (Figs. 31, 36, 40, 47, 53) but disappears ultimately. The cellular haustorium in C. lanatus and C. epigaeus remains 404 DhLm~ SINon healthy for a longer time but its haustorial efficiency is rather doubtful, and finally it also degenerates. In Edgaria darjeelingensis and Herpetospermurn pedunculosum the young endosperm usually shows two well-defined regions: (a)micropylar region of smaller cells and (b) the chalazal region of bigger cells (Fig. 43). In other cases, however, smaller micropylar endosperm cells become pro- gressively bigger towards the chalaza. The cellular endospelm in all plants continues its growth by cell division and cell enlargement. But after lhe formation of cordate embryo, it grows mainly by cell enlargement, and the divisions are confined to the peripheral cells only. The nuclei of the enlarging cells undergo interesting changes. With the decline of the haustorial activity, the peripheral cells of the cellular endosperm in the chalazal region bulge out, moie so in Cyclanthera, Dicoelospermum, Citrullus and Luffa. These cells in Luffa divide, foiming short cellular mounds which look like cellular haustoria tbrmed secondarily (Fig. 54). The endosperm consumes most of the nuccllus except its epideimis and a few hypodermal layers; and most of it is in turn utilised by the growing embryo. Only one or at places two layers of the endosperm finally surround the mature embryo. Behaviour of the endosperm nuclei during seed development.--The endosperm nuclei are originally 8-12 microns, oval or round, with a homogeneous sap, and one to three nueleoli (Fig. 54). As the endospeim grows, its central cells enlarge, and their nuclei also increase in size. They become 60 to 120 microns and lobulate (Figs. 56-58, 60-63, 64-75). Fusion of endosperm nuclei has also been observed in Cucumis sp. (Fig. 59). Simultaneously, the nucleoplasm becomes vacuolate and granular, developing a number of deeply stained particles. These vacuoles and particles subsequently increase in number and size. However, the nuclei of the t;eripheral cells which persist in a mature seed always remain small. During these nuclear changes, their nucleoli also grow in size, and become amoeboid (Figs. 62-64, 71, 72, 74). The appendages of an amoeboid nucleolus ultimately break up bringing about an increase in the number of nucleoli (Figs. 65, 72, 73, 75). The enlarging nucleoli develop one to three small vacuoles which increase in size and number during further development. Finally, the endosperm nuclei as well as other cell contents disorganise completely. Scott (1944, 1953) has also recorded similar changes in the endosperm nuclei of Echinocystis macrocarpa from the living material studied under-the phase contrast microscope. A Furthar Contribution to the Endosperm of the Cucurbttaceae 405

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34 3~ 36 37 3'3 .FIos. 22-37 The nuclei of the chalazal endosperm haustorium also undergo similar changes. They are observed to elongate and become wormiform (Figs. 66-70), measurihg 200--300 microns in Cyclanthera pedata, rt il interesting 406 D&LBIR SINGH to find that a haustorium beginning from its tip to the base presents all gradations in the nature of nuclei. The nuclei at the base may be elorlgated worm-like, while those at the tip small, and round or oval. Ultimately, the nuclei at the tip also become wormiform, show the change progressing from the proximal to the distal end of the chalazal haustorium.

DISCUSSION The structure and behaviour of the chalazal endosperm haustorium in the Cucurbitaceae has attracted considerable attention during the last decade (Chopra, 1953, 1954, 1955; Chopra and Agrawal, 1958; Johri and Roy Chowdhury, 1957; Singh, 1955, 1957, 1961 ; and Weiling and Sehagen, 1955). So far structure and development of the endosperm and its haustorium has been studied in 21 genera and about 46 species, mostly belonging to the subfamily Cucurbitoideae. Actinostemma tenerurn is the only member of Zanoniodeae whose endosperm has been investigated herein. Absence of the haustorium is recorded in Ctenolepis garcinii (Chopra, 1955; Singh, 1957) and Corallocarpus conocarpus (Present study). The haustorium varies in structure in different species and occasionally in the same species also. Table III presents the size and nature of haustorium in the species investigated so far.

Within the limits of a genus, the structure of the haustorium may be uniform or variable. Species of Luffa, Cucumis, Cucurbita and Trichosanthes show uniformity in size and structure of the haustorium to a greater extent while these are variable in Ctenolepis, Corallocarpus, Cyclanthera and Melothria (including Solena heterophylla). The largest haustorium is recorded in Seehium edule, being 19,000 microns long and 250 to 500 microns broad (see Table III).

(1957) proposed that the length of a haustorium determines its cellular or coenocytic nature. Chopra and Agrawal (1958) have further pointed out that the chalazal endosperm haustoria in the Cucurbitaceae can be arbitrarily grouped into two categories : (1) haustoria up to 1,500 microns remain coenocytic or may become ceilular, (2) haustoria longer than 1,500 microns always remain coenocytic. These categories find some support from the present study but it also reveals that size alone does not determine the nature of the haustorium. The haustorium, only 240--440 microns long, always remains coenocytic in Luffa echinata; this is also true for other species of Luffa which usually have the chalazal endosperm haustorium less than 1,000 microns long (see Table III). On the other hand, a haustorium ±1,000 A Further Contribution to the Endosperm of the Cucurbitaceae 437

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M 410 DALBIR SrN~H microns long invariably becomes cellular in Benincasa, Citrullus, Cocclnla and Corallocarpus. The chalazal endosperm haustorium has been described in only about 5~ of species and about 20~ of the genera in the family. Any conclusions, therefore, regarding its value in taxonomy would appear to be premature; nevertheless, some interesting facts have come to light. Solena heterophylla Lout. in subsequent taxonomic literature is reduced to Melothria heterophylla (Lour.) Cogn., but Jeffrey (1962) recognises this monotypic genus in his classification of the family. The haustorium in S. heterophylla is rudimentary and cellular, while it is long and coenocyticin Melothria lieosperma and M. maderas patana (see Table III). The size and the nature of the haustorium, therefore,

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l~os. 55-75 provides yet another character for delimiting this taxon. Miiller and Pax (1889) include Coccinia in the Sicyoideae and Edgarta in Melothrieae in their A Further Contribution to the Endosperm of the Cucurbitaceae 411

classification of the family. However, the position of Coccinia among the urtiovulate genera is most unnatural; Singh (1961) and Jeffrey (1962) recog- nise the affinities between Edgaria and Herpetospermum. A reference to Table III clearly reveals that size and nature of the haustorium in Coccinia and Edgaria fully justify their respective positions in the classification of the family by Jeffrey (1962). Citrullus fistulosus Stocks, indigenous to India, has been taxonomically treated as a variety of C. lanatus (Thunb.) Mansf. (syn. C. vulgaris Schrad.) even in recent literature (Chakravarty, 1959). Khoshoo (1955)who studied the cytotaxonomy of the Indian species of Citrullus indicates that biosystematically C. colocynthis and C. lanatus belong to one coenospecies and C. fistuIosus to another. The affinities between the former two taxa find support from their short, and cellular or coenocytie haustoria. The haustorium comparatively much shorter, maximum 333 microns long, always becomes cellular in C. fistulosus. Cucumis melo var. pubescens, C. melo var. momordica, and C. melo var. utzTissimus in recent taxonomic works reduced to parent species (see Chakravarty, 1959; Meeuse, 1962). In spite of the great variation in the size of their fruits and seeds, their chalazal endosperm haustoria are more or less similar. The peculiarity of Luffa, having fibrous, dry and operculate fruits, also reflects in its short yet coenoeytic endosperm haustorium (see Table III). In this respect, therefore, it stands apart from all other genera of the family studied so far. Jeffrey (1962) has created a new subtribe "Luffinae" under Cucurbiteae to include this genus. Weiling and Schagen (1955), on the basis of endosperm haustorium in Cucurbita maxima, C. pepo, C. mosehata, C. mixta, and C. fieifolia have also supported the existing view that C. moschata and C. mixta are not closely related. It may tentatively be concluded that the size and nature of the chalazal endosperm haustorium in the Cucurbitaceae reveal in some cases concordance to the taxonomic divisions, and its detailed study in many more species belonging to all the subtribes and tribes of the family may enable to draw some definite conclusions of taxonomic value.

SUMMARY The development and structure of endosperm is studied in 15 species belonging to I I genera of the Cucurbitaceae. A chalazal endosperm haustorium is recorded in all the plants except Coral[oearpus conocarpus. The endosperm is of Nuclear type. The embryo-sac enlarges after fertilization and differentiates into an uppcr dilated endosperm proper and a lower tubular caecum in all plants except C. conocarpus. Wall formation initiates in the cndosperm proper and is progressive and centripetal. 412 DALBIR SINGH

The size of the endosperm haustorium varies in different species and bears no relation to that of the endosperm proper and ovule. It becomes partly or completely cellular in Corallocarpus epigaeus; and is cellular or coenocytic in Citrullus lanatus. It is permanently coenocytic in the remaining plants and bears a bulbous base in Cucumis melo var. momordica, Edgaria darjeelingensis, and Herpetospermum pedunculosum. The haustorial activity of coenocytic haustorium declines after the embryo attains the heart-shaped stage and it finally collapses. The haustorial efficiency of the cellular haustorium is rathr doubtful. During advanced stages, the peripheral cells of the chalazal region of the endosperm proper bulge out. These divide and form short cellular papillae or mounds in Luffa species, appearing as secondary haustoria. The central cells of the endosperm enlarge and their nuclei undergo interesting changes before degenerating finally. The taxonomic significance of the chalazal endosperm haustorium is discussed from a comparative study of its structure in the members of different subtribes and tribes of the family.

AC KNOWLED'GEMENTS I am grateful to Dr. Bahadur Singh for guidance and interest, Dr. B. Tiagi for critically reading the manuscript, and to Professor C. V. Subramanian, Head of the Botany Department, University of Rajasthan, for ericouragement.

REFERENCES

Chakravarty, H. L. .. "Monograph on Indian Cucurbitaceae," Ree. bot. Sue. India, I959, 17, 1-234.

Chopra, R. N. .. "The endosperm in some Cucurbitaceae," Curr. Sei., 1955, 22, 383-84. .. "Occurrence of endosperm haustoria in some Cucurbitac.eae," Nature .(London), 1954, 173, 352-53. •. "Some observations on endosperm development in the Cucur- bitaceae," Phytomorphology, 1955, 5, 219-30.

~ and Agrawal, Saroj. .. "Some further observations on endo~erm haustoria in Cucurbitaceae," Ibid., 1958, 8, 194-20J. .. "Notes on Cucurbitaceae, including a ¢lamifl- Jeffrey, C. proposed new cation of the family," Kew Bull., 1962, 15, 337-71.

Johri, B. M. and Roy .. "A contribution to the embryology of Citrullus colocynthi: Chowdhury, C. Schrad. and Melothria maderaspatana Cogn.,'" New Phytol., 1957, 56, 51-60. ~o~oo. T. N. .. "Cytotaxonomy of Indian specieS of CitruUva," Cure. SoL, 1955, 24, 377-78. A Further Contribution to the Endosperm of the Cucurbitaceae 415

Meeu~, A. D.J. .. "The Cucurbitaceae of Southern Africa," Bothalia, 1962, 8¢ 1-112. Miiller, E. G. O. and Pax, F. .. "Cucurbitaceaej" in Engier and Prantl's Die naturlichen Pflanzenfamilien, Leipzig, 1889, 4 (5), 1-39. Scott, F.M. .. "Cytology and microchemistry of nuclei in developing seed of Echinocystis macrocarpa," Bot. Gaz., 1944, 105, 330-38. "The physical consistency of the endosperm nucleus of Echino- cystis mocroearpa," Phytmnm'photogy, 1953, 3, 66-76. $ingh, D. "Embryological studies in Cucumis melo L. var. pubescens Willd," J. Indian bot. Soc., 1955, 34, 72-78. "Endoslmm~ and its chalazal hau~torium in Cucurbitaceae," Agra Univ. J. Res., 1957, 6, 75-89. "Studies on endosperm and development of seeds in Cucur- bitaceae and some of its related families," Ibid., 1961, 10, 117-24. and Bhandari, M. M. "The identity of an imperfectly known hermaphrodite Luffa. with a note on related species," Baileya, 1963, 11, 132-41. Weiling, F. and Schagen, R. .. "13ber die praparation und Gestalt des Endosperm haustorium bei den grossamigen Kurbisarten," Ber. dtsch, bet Ge#., 1955, 68, 1-10.

EXPLANATION OF TEXT-FIGURES Fins. 1-21. Stages in the formation of the chalazal endosperm haustoria. Figs. 1-4. Corallo- carpus conocarpus, note the absence of chalazal endosperm haustorium. Figs. 5-10. C. epigaeus, the chalazal endosperm haustorium becomes partly or completely cellular. Figs. 11-21. Citrullua ianatua, the chalazal endosperm haustorium either becomes cellular or remains free nuclear (All figures from whole mounts); Figs. 1-4, 6, 7, 11, 13, 15, 17, 18, 20, semi-diagrammatic. Figs. 1-3, 5-7, 10,x65; Figs. 4, 9, 11, 13, 15, 17, 18, ×28; Figs. 12, 14, 16, 19, xll0; Fig. 20, ;<13; Fig. 21, x60). ch, chalazal endosperm haustorium; e, embryo; en, endosperm proper; pt. pollen tube. FIGs. 22-37. Stages in the formation of the chalazal endosperm haustoria. Figs. 22-25. Actinostemma tenerum. Figs. 26-29. Cucumis melo var. momordica. Figs. 30-32. Cucumls prophetarum. Fig. 33. Cyclanthera pedata. Figs. 34-36. Dactyliandra welwitschii. Fig. 37. Trichosanthes cucumerina. (All figures from whole mounts; Figs. 22, 24, 27-31, 33-37, semi- diagrammatic; Figs. 22, 27, ×28; Figs. 24, 31, 33-37, ×13; Figs. 23, 25, 32, ×110; Figs. 26, 30, x 48; Figs. 28, 29, × 33). FIGS. 38-54. Stages in the formation of the chalazal endosperm haustoria. Figs. 38--40. Dicoelospermum ritchiei. Figs. 41-44. Edgaria darjeelingensis. Figs. 45-47. Herpeto. aperraum pendunculosum. Figs. 48, 49. Luffa eehinata. Figs. 50, 51. L. hermaphrodita. Figs. 52-54. L. graveolens. (Figs. 38, 50 from sections, rest from whole mounts; Figs. 39. 42-47, 49, 51-53, semi-diagrammatic; Fig. 38, ×.266; Figs. 39, 40, 43--47, 53, ×13;-Figs. 41. 42, x28'; Figs. 48, 49, 51, 52, x80; Figs. 50, 54, ×110.) Fins. 55-75. Endosperm nuclei from developing seeds, for explanation ace text. Figs. 55-55. Citrullus lanatus, × 600. Fig. 59., Cucumis melo var. momordica, x600. Figs. 60-62. Dacty. liandra welwitschii, ×600. Figs. 63-70. Cyclanthera pedata, x600. Figs. 71-73. Herpete- opermum pedunculosum, .x600. Figt. 74, 75. Edgaria dar#elingemis, x600.