430 FERTILIZATION '. DEVELOPMENT OF EMBRYO. 



fecundation, however, a small number of peculiar corpuscles, which, 

 seem to be unwalled masses of viscid protoplasm, are seen lying 

 freely in this liquid, near the apex of the Embryo-sac ; these are 

 incipient Germ-cells, of which one only, the Embryonal Corpuscle, 

 is ordinarily destined to be fertilized. This act is accomplished by 

 the penetration of the Pollen-tube, which, when it has made its 

 way down to the ovarium, enters the Micropyle of the Ovule, and 

 impinges upon the apex of the Embryo-sac, which it sometimes 

 pushes before it in such a manner as to have given origin to the 

 idea that the tube enters its cavity : no such penetration, however, 

 really takes place ; and it is only by transudation through the 

 membrane of the Embryo-sac, as well as that of the Pollen-tube, 

 that the contents of the latter can reach the interior of the former. 

 As a consequence of this transudation (the influence of which seems 

 to be the same as that of the contact of the Antherozoids in the 

 Cryptogamia) the Embryonal Corpuscle is completed into a Cell by 

 the development of a Cellulose-wall around it ; and the production 

 of this Primordial Cell lays the foundation of the fabric of the 

 Embryo, which is developed from it like the brood that springs from 

 the Oo-spore of the Protophytes. 



321. The early processes of Embryonic Development correspond 

 closely with those which have been described as taking place through 

 the whole of the inferior tribes : for the Primordial Cell gives origin 

 by binary subdivision to a pair, this again to four, and so on ; it 

 being usually in the terminal cell of the filament so generated, that 

 the process of multiplication chiefly takes-place, as in the Confervse 

 (§ 249). The filament then begins to enlarge at its lower extremity, 

 where its cells are often multiplied into a somewhat globular mass ; 

 of this mass, by far the larger proportion is destined to be evolved 

 into the Cotyledons, or Seed-Leaves, whose function is limited to 

 the earliest part of the life of the young Plant ; the small remainder 

 is the rudiment of the Plumida, which is to be developed into the 

 Stem and Leaves ; while the prolonged extremity of the embryonic 

 filament which is directed towards the Micropyle, is the original of 

 the Radicle or embryonal Root. The mucilaginous protoplasm 

 filling the Embryo-sac, in which the Embryonal Corpuscle was im- 

 bedded, becomes converted by the formation of free cells, soon 

 after fecundation, into a loose cellular tissue, which constitutes 

 what is known as the Endosperm; this, however, usually deli- 

 quesces again, as the embryonal mass increases in bulk and presses 

 upon it.* 



322. In tracing the origin and early history of the Ovule, very 

 thin sections should be made through the Flower-bud, both verti- 



* A more detailed account of the Generative process in Phanerogamia 

 will be found in the article ' Reproduction, Vegetable,' in the "Cyclopedia 

 of Anatomy and Physiology," Supplement, p. 211. The most recent in- 

 formation on the subject will be found in Prof. Hofmeister's " Neue 

 Beitrage zur Kentniss dcr Embryo-bildung der Phanerogamen," Leipsig, 

 1859-61. 



