766 SUMMARY OF CimRENT RESEARCHES RELATING TO 



cavity of tho embryo-sac with tissue may take place in three different 

 ways, viz.: — (1) Tho endogenous tyjic, by the division of a nucleated 

 mass of protoplasm which fills up the cavity, as in Eranthis; (2) By the 

 formation of tissues, which commences at the periphery on all sides, and 

 advances centripetally ; this occurs in other Eanunculaceaa, as Hellehorus, 

 Ni'jcUa, Baminculus, Adonis, and Caltha, in the Rosacea) [Cotoneaster), 

 Umbellifera) (^Archangelica), Malvaccro (Mnlva, Uibiscus^), certain Legu- 

 minosa) (Hij^pocrcpis, Coronilla, Anthyllis, Lotus), and some Papaveracea) 

 (^Glancium, Chelidonium, Hypecoum, Eschscholtzia, Fumaria), also, in a 

 modified way, in Bocconia, Scabiosa, and Euphorbia ; (3) A formation of 

 tissue commencing at the periphery on one side only, at the micropylar 

 end, and leaving the chalazal part at first more or less unaffected, but 

 afterwards advancing towards it; this was observed in many Leguminosaa 

 (Cytisus, Sarothanmus, BapAisia, Hedysarum, Onohrychis, Trigonclla, 

 Galega, Colutea (?) ), and in Polygonacea3 (Fagopyrum, Polygonum, 

 Bumex). 



In the third case the formation of parenchyma from the micropylar 

 end may be so sparing as not entirely to envelope the embryo, as in the 

 CaryophyllaccfE ; or the enveloping tissue may be broken through and 

 ruptured before it reaches the hinder part of the embryo-sac, as in 

 Chenopodiaceje, Nyctagiuese, Phytolacca, and some Lcguminosa). A 

 peculiar modification of this process occurs in those cases where it is 

 localized to some other part of the embryo-sac than its apex, namely, in 

 a concavity, as in strongly camjiylotropous ovules ; this is characteristic of 

 the majority of species of Lupnnus. Tropaeolum is peculiar in the parietal 

 layer of protoplasm not breaking uj) into cells. 



These various modes of formation of endosperm only correspond to a 

 certain extent to systematic aflSuities ; thus Eranthis differs from the 

 other Helleboreas, and the Lcguminosa) are broken up into several 

 groups. Free cell-formation, in the narrowest sense of the teim, has 

 not at present been observed ; the ordinary process being an intermediate 

 one between that and true cell-division. 



The author points out various essential differences between the 

 process of the formation of the endosperm in Dicotyledons and that of 

 the primary and secondary prothallium in the hetcrosporous Vascular 

 Cryptogams, such as Selaginella. In Marsiliacete and Salviniaceae, and 

 in the formation of the primary prothallium in Selaginella, a true process 

 of cell-division takes place. The prothallium of Coniferse, in which 

 there is not the sharp differentiation into two distinct portions which 

 occurs in Selaginella, is at first formed by free cell-formation round 

 distinct nuclei; though cell-division afterwards takes place in tho 

 formation of the tissue. 



The endosperm-tissue has two distinct functions, separated from one 

 another in time by a period of rest. In the first place it serves as 

 a reservoir for the reserve-substances subsequently consumed by the 

 embryo ; and in the second place it conveys nutrient materials to the 

 embryo on its free surface during the period of its development. In some 

 cases, however, this latter function is j^erformed vicariously by the fluid 

 of the embryo-sac, or a portion of the material is conveyed by the enlarged 

 base of the embryo, whether developed into a suspensor or not ; but in 

 these cases the endosperm always co-operates in the conveyance of the 

 nutrient material. 



