and its relation to that in the Animal Kingdom. 447 



means this takes place, cannot be quite perceived, unless we 

 assume that such a dilution of the contents of the pollen-tube 

 as must occur here before it can reach a germinal vesicle, does 

 not remove its fecundating properties, or is perhaps even actu- 

 ally necessary for their operation. Such cases alone may yet 

 leave some hope for those who, in contradiction to the negative 

 results of all existing observations, still expect, fi-om analogical 

 reasoning alone, to find morphological fecundating elements — 

 spermotozoids — in the Phanerogamia. 



In the foregoing we have discussed only an endosmotic transit 

 of the contents of the pollen-tube into the embryo-sac and ger- 

 minal vesicles. Earlier observers, as Meyen* and Cobboldf, and 

 also, quite recently, HenfreyJ, have been inclined to assume 

 that a copulation or conjugation, analogous to that of the Con- 

 fervse, takes place between the end of the pollen-tube and the 

 embryo-sac, thus furnishing a direct passage for the transit of 

 the contents of the pollen-tube. We are certainly not of opinion 

 that such a condition is impossible, but must at the same time 

 own that we have never yet been able actually to observe any- 

 thing of the kind. If such negative observations have but a 

 very inferior value, yet on the other side there exist no positive 

 proofs; and, in addition to this, the circumstance, that in the 

 ordinarily occurring condition of the germinal vesicle to be 

 fecundated, standing at a distance from the end of the pollen - 

 tube, such an arrangement would not cause a direct passage of 

 the fecundating substance to the mass of germinal substance — is by 

 no means calculated to render us more inclined to adopt the 

 hypothesis in question. 



However this may be, so much is ascertained,^ — that the con- 

 tents of the pollen-tube form the analogue of the spermatozoids, 

 the germinal vesicle that of the ovum ; that the fecundating pro^ 

 cess of the Phanerogamia corresponds completely to that of the 

 Cryptogamia, and to that of Animals. 



Are we justified in distinguishing in the germinal vesicle of 

 the Phanerogamia contents and membrane, like the vitellus and 

 its membrane ? It might almost appear so, since we see that in 

 no case does the original membrane of the germinal vesicle take 

 part in the structure of the embryo itself. Yet, since the mode 

 of formation of the latter is so different from that of the animal 

 embryo, it may be going too far to try to find analogies here. 



It remains only for us to estimate the import of the conjuga- 

 tion of the Alga. Areschoug^s observations have removed every 

 difficulty that might have prevented us from regarding it as a 

 true process of fecundation. If some room still remain for doubt 



* Pflanzenphysiologie, iii. p. 314. f L. c. supra. 



X L. c. svpra. 



