.ORIGIN OF THE EMBRYO. 305 



proved in all points by a series of elaborate investigations made by 

 Mirbel, Amici, Giraud, Mold, Hofmeister, Unger, Tulasne, Ilenfrey, 

 and Radlkofer. So that — passing by the whole history of this long 

 discussion, and merely appending some references to the more im- 

 portant publications upon the subject * — we need only state here, 

 in the most general terms, the principal facts which are now held 

 to be established, viz.: — 



579. The pollen-tube terminates on the outer surface of the 

 embryo-sac, or sometimes, perhaps, forces its way into it. Ordina- 

 rily its extremity becomes firmly adherent to the surface of the 

 embryo-sac, and it appears to remain closed. Ilenfrey, indeed, is 

 led to suppose that the membrane of the pollen-tube and that of the 

 embryo-sac are absorbed at the point of contact, and that the former 

 thus discharges its contents into the cavity of the latter ; but this is 

 merely an unproved inference, suggested by the analogy of what is 

 now known of the process of fecundation in Cryptogamous plants. 

 At present it appeal's most probable that the contents of the pollen- 

 tube are drawn into the embryo-sac by endosmosis. However this 

 may be, shortly after reaching the embryo-sac the pollen-tube be- 

 comes empty, and decays or withers away. Meanwhile the body 

 which by its development is to give rise to the embryo appears in 

 the embryo-sac independent of the pollen-tube. According to most 

 investigators it generally appears before the pollen-tube has entered 

 the ovule. (The high authority of Tulasne, however, is thus far 



* Schlcidcn first published his famous theory in Wiegmann's Arehiv, 1837, 

 and in Acta Nova Acad. Nat. Cur., Vol. 19. It was extended and defended in 

 his systematic works, — and especially by Schacht in Tram. Netherlands Insti- 

 tute, 1850, in Bol. Zeitung, 1855 (transl in Ann. Sci. Nat. of that year), in his 

 Beitiiir/e Anat. §• Phi/s., in his work on the microscope, of which an Engli.-h 

 translation by Dr Currcy was published in 1855, and in the Rcgensberg 

 Flora, 1855 (Ann. Sri. Nat. 1855). Sec also Dcecke in Hot. Zeihtng, 18f.5 

 {Ann. Sri. Nat., 1 c ) On the other side of the question the most important of 

 the recent publications, since the appearance of Mold's Principles of the Anatomy 

 and Phys.o'o'jy of the Va/etable Cell, in the English translation (1852), and tho 

 article Ovule in the Miaor/iapluc Dictionary by Ilenfrey, arc : Hofmeister, in 

 Flora, May, 1855, and Mold, in Dot Ze.itung, June, 1855 (both reproduced in 

 Ann. Sci. Nat., ser. 4, Vol 3, 1855); Tulasne, in Ann Si. Nat., scr. 4, Vol 4, 

 1855, being the complement of his great memoir published in the same journal 

 (scr. 3, Vol. 12, 1849) ; Radlkofer, Die Brfruchtunrj der Plianmy/amien, Lcipsic, 

 1S56 ; Ilenfrey, Development of the Ovule of SanUilum lubuia, &c , in Trans. Linn. 

 Soc., Vol. 22, part 1, 1856. 



2G* 



