( 829 ) 



regular pollination among these plants is probably not so very large, 

 and that in consequence of this so ntiany ovules ultimately abort. 



I now pass on to describe what I have seen of the fertilisation 

 itself, and must remark, that I have but rarely observed anything 

 of the penetration of the pollen-tubes; to some extent this is probably 

 a result of the process of fixation, during which such tender, thin 

 structures readily shrivel up ; at the same time the staining does not 

 succeed well. In any case 1 can however state, that the pollen-tube 

 penetrates through the micropyle, and then reaches the egg-apparatus 

 by passing between two epidermal cells of the nucellus. In one case 

 I observed two nuclei in the top of the pollen-tube, one of which 

 appeared to be a generative and the other a tube-nucleus. In another 

 case I saw a nucleus, which had a much elongated appearance, and 

 was constricted in the middle, so that there might have equally well been 

 two generative nuclei. Taking all the cases, which I have seen, into 

 account, I am led to the view, that the conditions in the top of the 

 pollen-tube are normal, so that there are two generative nuclei and 

 one tube-nucleus. In the actual process of fertilisation, the top of the 

 pollen-tube unites with one of the synergids ; the synergid and espe- 

 cially also the egg undergo at the same time peculiar changes in 

 shape, somewhat resembling amoeboid movements. What further 

 happens in the synergid cannot readily be made out, because its 

 contents stain very strongly and become highly refractive. I never- 

 theless also succeeded in this case in observing the main features of 

 the process. At least one nucleus of the pollen-tube penetrates into 

 the synergid and assumes, in so doing, a more or less vermiform 

 shape. Thereupon a fusion of the synergid with the egg takes place, 

 so that the protoplasts communicate with each other at least at one 

 spot. This communication does not last long, but during it one of 

 the generative nuclei evidently penetrates into the egg-cell; anyhow 

 stages are found later, in which two nuclei lie close to each other in 

 the egg. Still a little later these are found in contact, and afterwards 

 they are found fused in such a manner, that the origin from two 

 nuclei can still be seen. 



The fertilized ovum now rapidly enlarges, while all other cells 

 in its neighbourhood are crowded out. As the epidermal cells of the 

 nucellus have generally aborted, this large cell lies more or less by 

 itself in the endostomium, almost filling it up. By the first division 

 wall there is formed a bladder-like basal cell, which remains in the 

 cavity, and a smaller one, which is gradually pushed forward into 

 the pseudo-embryosac. This cell now undergoes some divisions, in 

 which the walls are formed perpendicular to the long axis of the 



56 



Proceedings Royal Acad. Amsterdam. Vol. X. 



