44G Dr. L. Radlkofer on Fecundation in the Verjctahle Kingdom, 



In the case where the point of attachment of the end of the 

 pollen-tube on the outside of the embryo-sac corresponds, not 

 to the point of attachment on the inside of the v.all of a germinal 

 vesicle developed into a suspensor, but to the point of attach- 

 ment of a destroyed germinal vesicle — it can scarcely be decided 

 whether the transit of the contents of the pollen-tube into the 

 former is effected through the intermediation of the latter, or 

 through an exudation of the contents of the pollen-tube over 

 the embryo-sac, which can be shown to occur to a certain extent. 



When one sees how the germinal vesicle lying immediately 

 opposite the end of the pollen-tube, the contents of which assume 

 exactly the optical character of the contents of the pollen-tube, is 

 aborted in certain plants with apparently unexceptional regularity, 

 while the other, seemingly less favourably situated, is developed, 

 the idea is not far-fetched, that the further development of the 

 former is arrested actually by the transfer to it of too large a 

 quantity of the dense fluid contents of the pollen-tube. At pre- 

 sent we are, indeed, ignorant of the more intimate relations in 

 which the growth or re-formation of a cell-membrane stands to 

 the character of the cell-contents; yet we may assume that both 

 (putting all else out of the question) maybe rendered impossible 

 by too slight or by too great a concentration of the formative fluid. 

 It might even be supposed that the contents of the pollen-tube 

 must here first undergo dilution in the one germinal vesicle, to 

 enable it to fertilize the other ! Strange as this arrangement may 

 appear to our existing notions, yet, even if a perfect analogy ought 

 scarcely to be sought beyond the limits of the vegetable king- 

 dom, a phsenomenon may be referred to which admits of the 

 supposition, that in the fecundation of the animal ovum, also, it 

 may be by no means left to accident how much of the fecun- 

 dating substance mingles with the vitellus. When we observe, 

 namely, in the ova of the frog, which come in contact on all sides 

 with a great quantity of spermatozoids, that the vitelline mem- 

 brane is only penetrable by them at a definite and limited spot, 

 while no great resisting power can be attributed to this on phy- 

 sical grounds, it may be admissible to allow the above idea a 

 place in the discussion of this question. 



Lastly, by what means the mixture of the fecundating sub- 

 stance with that to he fecundated takes place in the case where 

 the end of the pollen-tube touches the embryo sac at a distance 

 from the points of attachment of the germinal vesicles, and 

 therefore does not come in contact with any of them, as strangely 

 happens in various plants, according to Hofmeister's recent in- 

 vestigations, which I believe are not yet published*, — by what 



[* Hofmeister, Embrvo-bildung der Phanerogamen. Jabrb. fiir wiss. 

 Botanik, i. p. 180. Berlin, 1857.— A. H.] 



