( aw ) 



Oen. Luw. with what R. Beer 1 ) has described for Oenothera longiflora. 

 When the pollen-grains are almost mature, the generative and the 



vegetative nucleus are formed by division ; the generative nucleus, 

 which is the smaller, and is surrounded by a quantity of plasma, 

 then applies itself to the wall; the vegetative nucleus remains in the 

 middle of the grain. The division of the generative nucleus into two 

 probably takes place in the pollen-tube. 



The pollen-tube penetrates through the micropyle and through the 

 nucellar tissue. It seems as if in this place the nucellar tissue already 

 becomes in advance disorganized. Since, when the pollen-tubes 

 penetrate, the synergids are already completely disorganized and 

 stain very deeply, and since in the nuccllus, at the spot where the 

 pollen-tube has penetrated, dark coloured remnants are everywhere 

 visible, I have not succeeded in observing the division of the gene- 

 rative nucleus Fertilisation itself was however clearly observed. A 

 double fertilisation takes place; one nucleus penetrates into the egg- 

 cell and applies itself against the nucleus; the generative nucleus is 

 at that time round, but smaller than the egg-nucleus, although it 

 probably becomes somewhat larger before fusion. The other gene- 

 rative nucleus, which presents the same shape, applies itself to the 

 polar nucleus. The fusion between the polar nucleus and its gene- 

 rative nucleus takes place more rapidly than that of the other gene- 

 rative nucleus with the egg-nucleus. The fertilized polar nucleus 

 now soon divides, so (hat frequently there are already a number of 

 endosperm nuclei before the egg-nucleus has completely coalesced 

 with the generative nucleus, and before the egg-cell has a wall of 

 its own. The fertilized egg-cell grows out to a short suspcnsor, and 

 an embryo with distinct octants. Endosperm nuclei then already lie 

 along the whole of the wall of the embryosac. Afterwards this 

 endosperm however again disappears. 



In Oenothera Lamarckiana the endosperm is tlierefore formed 

 from inn' fertilized polar nucleus. 



In mature stamens very many sterile grains are found in the 

 pollen: in young fruits there occur between the developing seeds a 

 fairly large number of ovules, which are not undergoing development. 

 hi both cases the sterility arises after the reduction division. Whilst 

 in all embryo-sac mother-cells the reduction division takes place 

 normally, there are still many ovules in which the upper tetrad cell 

 also degenerates, this degeneration being accompanied by much the 

 same phenomena as occur regularly in the three lower cells of the 



'I On the developmenl <>t' the pollen grain ami anther of some Onagraceae, 

 Rudolf Beer. Beih. zum but. Gentr. blalt 1905, 19 1. 



