REPRODUCTION, VEGETABLE (VEGETABLE OVUM). 



251 



which is not evident, but which seems ana- By continuous cell multiplication an organ 

 logous to the suspensor, presently to be is formed, in which may be distinguished a 

 mentioned, meanwhile decays away."* 



Fig. 199. 

 Fig. 197. 



Ovule of the same at the period of impregnation, 

 x, the external integument ; c, the internal, which 

 immediately surrounds e, the embryo-sac. The 

 pollen tube p, after passing the wide exostome 

 becomes sensibly narrowed as it penetrates the 

 canal leading to the embryo-sac, with the out- 

 side of which its termination is in contact. 180 

 diam. 



108. The anther and the pollen cell. The 

 history of the development of the anther is 

 remarkably uniform among the different families 



Fig. 198. 



The same, some time afler impregnation. 

 The remains of the pollen tube are observed to be 

 still adherent to the sac. The rudiment of the 

 embryo exhibits itself as a somewhat pear-shaped 

 cell, divided towards its upper part by a succes- 

 sion of transverse septa, into numerous compart- 

 ments. The lowest of these, larger and more 

 granular than the rest, is the parent-cell of the 

 embryo. 180 diam. (The above, from 191 to 198 

 inclusive, are original.) 



of Phanerogamia. It at first appears in the 

 young flower-bud as a cellular papilla, which 

 grows out laterally from the floral axis. 



* Henfrey, On the Reproduction of the higher 

 Cryptogamfa, and the Phanerogamia. Annals of 

 Nat. Hist., June, 1852. 



Further developed embryo. (Orchis Morio.") 



The embryo-sac is no longer distinguishable. The 

 spheroidal embryo which completely occupies 

 the cavity of the ovule is surmounted by a fila- 

 mentous prolongation, which projects through the 

 micropyle. 150 diam. (Henfrey.) 



central cylindrical column (connective), along 

 the antero-lateral aspects of which are at- 

 tached two larger cellular masses; the outer 

 surface of each is marked by a vertical furrow, 

 indicating its division into two halves, which 

 are the rudiments of the future facuti. In 

 each half a single axile vertical column of 

 cells soon becomes distinguished from those 

 surrounding them by their greater size and 

 granular contents. In each of these cells 

 the nucleus disappears, and is replaced by 

 two others, this being followed by a division 

 of the cell contents (primordial membrane), 

 which results in the formation of a new 

 cell round each nucleus. By the repeti- 

 tion of this process a mass of cells the 

 parent-cells of the spores is formed, which 

 occupies the centre of each rudimentary 

 loculus. The next change observed is the 

 thickening of the walls of the parent-cells by 

 gelatinous deposition on the interior surfaces. 

 This is followed in all of them by disappear- 

 ance of the nucleus, and consequent division 

 of the contents of the cell (primordial mem- 

 brane) into two portions, each surrounding a 

 new nucleus. These, however, are only trans- 

 itory formations, and are soon succeeded by 

 four permanent nuclei, which are placed 

 towards the four angles of a regular tetrahe- 

 dron, each invested with a primordial sac con- 

 taining a granular mucus, on the surface of 

 which is soon secreted a gelatinous layer. In 

 this manner the parent cell is divided into four 

 compartments the so-called special parent 

 cells of the pollen grains. Within each com- 

 partment is now formed a new cellulose mem- 

 brane on the surface of the primordial utricle. 

 This is transformed into a resistant and co- 

 loured tegument, which is the outer mem- 

 brane of the pollen grain, and exhibits various 

 projections of its surface, which differ ac- 

 cording to the species. 



109. While these changes are taking place 

 in the central mass of each loculus, the tissue 

 forming its wall is transformed into a capsule 

 of three distinct cellular lavers. Tiie inner 



