644 SUMMARY OF CURRENT RESEARCHES RELATING TO 



suspensor often temporarily contain starch. Immediately after re- 

 ceiving this supply of food-materials, the embryo, which had hitherto 

 undergone very little change, alters in form and increases greatly in 

 size, assuming the ordinary globular form of the embryo of Orchidese. 

 In Peristylus the embryo appears to receive the whole of its nutriment 

 in this way, while in European orchids a portion is derived from the 

 ovule itself. 



Avicennia officinalis presents this peculiarity : that the two cells 

 formed by division of the sister-cells of the embryo-sac are not, as is 

 elsewhere the case, resorbed or compressed. A short time after 

 fertilization the embryo-sac contains endosperm-cells which surround 

 the embryo, and one large cell reaching to its apex, which the author 

 calls the cotyloid cell. Subsequently the endosperm gradually emerges 

 from the embryo-sac ; the embryo undergoes in the meantime further 

 development, and after a time is covered only on one side by a thin 

 layer of endosperm. In this layer a cleft is formed through which 

 the cotyledons project, while the lower end of the embryo remains in 

 the endosperm. The upper part of the cotyloid cell, together with 

 the endosperm, projects out of the micropyle ; while its lower part, 

 still enclosed in the ovule, puts out protuberances on all sides into 

 its tissue and into the placenta, which, after a time, it completely 

 permeates like a mycelium. The cotyloid cell undoubtedly performs 

 the same function as the suspensor in orchids, viz. that of a nutritive 

 organ, carrying to the embryo, through the endosperm, the nutritive 

 substances contained in the ovule and in the placenta. 



Embryogeny of the Leguminosse.* — The following are the main 

 results of an extensive series of observations made byL. Guignard on 

 the development of the embryo and embryo-sac of a number of plants, 

 mostly belonging to the Leguminosas. His general conclusions do 

 not confirm the theory of some writers that the nucellus of the embryo- 

 sac is the homologue of a pollen-grain or spore. 



The axile hypodermal cell of the nucellus divides horizontally into 

 two cells of variable size, the apical and the subapical cells. The 

 apical cell either remains undivided or gives rise to a tissue of varying 

 thickness, the " calotte." This tissue is especially developed in the 

 Minioseas and Cassalpinieas at the period of impregnation ; in the latter 

 group it remains for a time after impregnation. The subapical cell 

 (primordial mother-cell of Warming) may either remain undivided, and 

 develope directly into the embryo-sac (Medicago, Melilotus), or it 

 divides into a variable number of superposed cells, the lowermost of 

 which (the true mother-cell) displaces the others, and alone developes 

 into the embryo-sac. Cases are described in which the number of 

 these cells is two, three, and four respectively. The order of formation 

 of the cell- walls is usually basipetal ; they may be thicker or not than 

 the neighbouring cell-wall. With possibly the single exception of 

 Acacia albida, the embryo-sac is invariably the product of the lower- 

 most cell, never of the fusion of two cells. 



* Ann. Sci. Nat. (Bot.) xii. (1881-2) pp. 1-166 (8 pis.). Of. this Journal, iii. 

 (1880) p. 473 ; i. (1881) pp. 69, 260, 620 ; ante, p. 64. 



