FORMATION OF THE EMBRYO. 319 



578. Two or more embryos are frequently found in the same 

 seed, in the Orange, the Onion, and many other cases. There 

 are generally two embryos in the seed of the Mistletoe ; and there 

 is constantly a plurality of embryos in Pines and other Gymno- 

 spermous plants (560), though all but one are more commonly 

 abortive or rudimentary.* 



579. Contemporaneous with the production of the embryo, a 

 cell-formation takes place in the mucilaginous liquid contained in 

 the embryo-sac, soon filling the space with an exceedingly soft and 

 delicate parenchyma, proceeding from the wall of the sac inwards. 

 Sometimes the enlarging embryo, as it grows, obliterates this deli- 

 cate, half-fluid tissue, is nourished by its contents, and at maturity 

 fills the integuments of the seed completely. In other cases, the 

 growth of the embryo in the seed is arrested before it fills the em- 

 bryo-sac : then this new tissue that surrounds it, solidified by inter- 

 nal deposition, or with its cells filled with starch, &c., becomes 

 permanent, and forms the albumen of the seed (627) ; or some- 

 times this cellular growth and deposit of nutritive matter take 

 place in the persistent body of the nucleus of the ovule, external 

 to the embryo-sac, as in Nymphsea. 



580. With the development of the embryo, the ovule becomes 

 the seed. Its further history should follow that of the fruit. 



this point, either from a sort of" dedoublement " of the membrane of the em- 

 bryo-sac, or from a nucleus adherent there; and he inclines to think that its 

 formation does not precede the conjunction of the pollen-tube with the em- 

 bryo-sac, but that it is the first visible result of this union. And, calling to 

 mind that Unger met with free cells in the unimpregnated embryo-sac of 

 Hippuris vulgaris, formed from free and floating nuclei, but which were al- 

 ways resolved before the appearance of the real embryonal vesicle, he sug- 

 gests that the free cells seen by Hoffmeister may be of the same kind. M. 

 Tulasne plausibly considers that the embryo-sac is the cell which receives 

 the fluid of the pollen, and that in its cavity, therefore, the contents of two 

 cells are commingled; the result of which union gives rise to the embryonal 

 vesicle, or potential embryo, endowed from the first with the new specific 

 force which it manifests in its ulterior development. We can only refer the 

 inquirer to this original memoir; an abstract can hardly be made intelligible 

 to the uninstructed reader, without the plates. 



* In Conifers (at least in the Pines) the embryo is not developed from the 

 embryonal vesicle until long after the cavity of the embryo-sac is filled with 

 the cellular tissue that forms the albumen of the seed ; and its formation ap- 

 pears to be in other respects peculiar. 



