400 STRUCTURE OF PHANEROGAMIC PLANTS. 



but nearly all other Vegetable Physiologists who have examined 

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

 clusion, namely, that the embryo 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" w r as 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 " pro thallium" of the 

 higher Cryptogamia. 1 



25T. 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 



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

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

 tion on this controverted question, the Author may be permitted to refer to his ' Prin- 

 ciples of Comparative Physiology," 4th Ed. 501-505. Some recent discussion on 

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

 et seq. 



