400 STRUCTUKE OF PHANEROGAMIC PLANTS. 



but nearly all othei" Vegetable Physiologists who have examined 

 the question with sufficient care, have come to a different con- 

 clusion, — namely, that the embiyo is the product of a cell-multi- 

 plication within the " embryonal vesicle," which seems to be 

 fertilized by the transudation of the contents of the pollen-tube, 

 just as the embryonal vesicle within the archegonium of the 

 Ferns is fertilized by the contact of the antherozoids (§ 219). 



256. The early processes of development, too, correspond 

 closely with those which have been described as taking place 

 through the whole of the inferior tribes ; for the primordial cell 

 that is formed within the embryonal vesicle as the result of its 

 fecundation, gives origin by transverse fission 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 (§ 198). 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 " plumula," which is to be developed within 

 the stem and leaves ; while the prolonged extremity of the em- 

 bryonic filament, which is directed towards the micropyle, is the 

 original of the "radicle" or embryonic root. The mucilaginous 

 protoplasm filling the "embryo sac," in which the "embryonal 

 vesicle" was imbedded, 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, how- 

 ever, usually deliquesces again, as the embryonic mass increases 

 in bulk and presses upon it ; and its development is of interest, 

 chiefly because it may be shown, by the curious intermediate 

 phase presented by the Lycopodiacece and Coniferce (§ 221), that 

 this endosperm is the equivalent of the " proth allium" of the 

 higher Cryptogamia.^ 



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

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

 cally and transversely ; but when the ovule is large and distinct 

 enough to be separately examined, it should be placed on the 

 thumb-nail of the left hand, and very thin sections made with a 

 sharp razor ; the ovule should not be allowed to dry up, and the 

 sections should be removed from the blade of the razor by a 

 wetted camel-hair pencil. The tracing downwards the pollen- 

 tubes through the tissue of the style, may be accomplished by 



* For a more detailed account of the Generative process in ordinary Phanerogamia 

 and in Coniferse, as well as for references to the principal original sources of informa- 

 tion on this controverted question, the Author tnay be permitted to refer to his " Prin- 

 ciples of Comparative Physiology," 4ih Ed. §§ 501-50S. Some recent discussion on 

 the same subject will be found in the "Ann. des Sci. Nat." 4ifeme Ser. torn, iii, p. 188 

 et seq. 



