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 hausto- rium 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 divi- sions, 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 6 ."i?i J F/os. 1-21 ,4 Further Contribution to the Endosperm of the Cucurbitaceae 403 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.