only one of them attains its full development. The Endosperm arises by free 

 cell-formation long before fertilisation in the embryo-sac which is distinguished by 

 its firm wall; but the cells soon become combfned into a tissue and increase by 

 division. Within this mass of tissue, corresponding to the endogenous prothallium 

 of Selaginella, arise the Archegonia (or Corpuscula^) in larger or smaller numbers. 

 Strasburger states that each of these bodies is formed from an endosperm-cell 

 lying at the apex of the embryo-sac, which increases considerably in size and 

 produces the neck and central cell of the archegonium by division. According 

 to the same authority a small upper portion of the central cell beneath the neck 

 is even separated as the canal-cell. Whether, as Strasburger asserts, the whole 

 contents of the central cell are to be considered as the oosphere, or whether, as 

 Hofmeister thinks, the embryonic vesicles arise in it by free cell-formation, must for 

 the present remain unsettled; although the first-named opinion would correspond 

 more closely with the analogy in other respects so remarkable with the heterosporous 

 Vascular Cryptogams-. After the pollen-tube has penetrated the tissue of the 

 nucleus and forced itself as far as the archegonium (corpusculum), where its fertilis- 

 ing material is conveyed to the central cell by diffusion, the Pro-embryo is formed 

 by division of a cell that lies in the lower part of the central cell. The pro- 

 embryonic cells are at first small, but the middle or upper ones develope into long 

 Suspemors, which, pushing the lower ones before them, break through the central 

 cell below, and penetrate into a softened part of the endosperm. Sometimes the 

 suspensors which are produced side by side separate, and each produces at its apex 

 a small-celled rudiment of an embryo. On this account, and also because several 

 archegonia are often fertilised in one endosperm, the unripe seed contains several 

 rudimentary embryos of which, however, only one usually increases greatly in size, 

 the others withering away. 



During the development of the embryo, the endosperm becomes filled with 

 nutrient materials and increases greatly in size ; the embryo-sac which encloses it 

 grows at the same time, and finally entirely absorbs the surrounding tissue of 

 the nucleus; the integument, or an inner layer of it, becomes developed into a 

 hard shell, while frequently (in naked seeds) its outer mass of tissue becomes 

 fleshy and pulpy and gives the seed the appearance of a drupaceous fruit {e.g. 

 Cycas, Salisburia). The effect of fertilisation not unfrequently extends also to the 

 carpels or other parts of the flower, which grow considerably, forming fleshy or 

 woody coatings to the seeds, or cushions beneath them. 



The ripe Seed is always filled with the endosperm, in which the embryo lies 

 and is distinctly differentiated into stem, leaves, and root. It fills up an axial 

 cavity of the endosperm, is always straight, its radicle being turned towards 



^ [The central celLs of the archegonia of Gymnosperms were discovered by Robert Brown in 

 1834. He called them corpuscula or embryoniferous areolae (Miscellaneous Botanical Works, 

 vol. I. pp. 567 and 570). The structure of the neck of the archegonium was made out by Hof- 

 meister, who applied to it the term rosette (On the Higher Cryptogamia, p. 411). Archegonium 

 and corpusculum do not seem exactly synonymous, since the latter, properly speaking, is only 

 equivalent to the central cell of the former. Henfrey termed the central cells ' secondary embryo- 

 sacs ' (Elementary Course, 2nd edition, p. 608). — Ed.] 



^ More will be said on this subject under Coniferce. 



