Plants, and Parthenogenesis. 201 



One, or, it may be, two of these free cells attach themselves 

 to the wall of the embryo-sac, with which the pollen-tube is in 

 contact ; and thereupon a process of cell-multiplication com- 

 mences. Not seldom this process goes on for a time in the two 

 germinal cells which may be present; but as a rule, one of 

 them preponderates, and alone proceeds in forming the germinal 

 mass (PL X.). 



What part the pollen-sac takes in the process — whether its 

 wall, which separates the germinal cell and the embryo-sac, be 

 absorbed, or whether its contents, on becoming fluid, are simply 

 diffused through it by exosmosis — cannot be satisfactorily decided 

 by direct examination. 



The larger proportion of the rudimentary cells contained in 

 the fluid of the pollen-tube at the time this comes into contact 

 with the embryo-sac serves for the formation of the albumen 

 which is disposed around the growing germ (PI. X.). 



That the embryo could be formed without the action of the 

 pollen-tube, as Radlkofer and Braun assume because Radlkofer 

 and Deeke frequently failed in detecting the pollen-tube, is an idea 

 no one will accept who is conversant with this kind of investi- 

 gation, which, in spite of the greatest dexterity and practice, 

 may frequently fail to exhibit in many plants the pollen-tube, 

 which nevertheless undoubtedly exists. 



The interesting question, whether, for the complete formation 

 of two germs which are frequently at first simultaneously deve- 

 loped, the action of more than one pollen-tube is necessary, still 

 remains to be answered. 



The germinal cells appear, at the time of their first forma- 

 tion, like very delicate-walled vesicles (termed vacuoles) ; indeed, 

 they seem to be present in the embryo-sac before the pollen- 

 tube reaches it ; at least, these cells are often to be seen when 

 the pollen-tube is undiscoverable, although this certainly can 

 never afford evidence that it actually does not exist. 



In some of the free swimming-vesicles, whose walls become 

 thicker and more perceptible, a new vesicle arises, which is usu- 

 ally called the nuclear corpuscle, because the free swimming- 

 cells which contain these very small secondary (daughter-) cells 

 have been distinguished as cell-nuclei, on the supposition that a 

 cellulose-layer is deposited around them as the membrane of a 

 cell which served as nucleus to this originally existing cell. 

 This, however, is not correct ; for, on the contrary, the mem- 

 brane itself, the vesicle contained within it, and the daiighter- 

 cells or the nuclear corpuscles extend themselves simultaneously 

 by means of cellulose, and one or several small new cells make 

 their appearance in them. 



