550 



PREFERENTIAL FERTILIZATION IN 



Tabel I 



Gamolysis of female gametes of 0. hybr. lucida. 



It is evident that in the ovaries of 0. lucida the ovules of the 

 0. deserens type are far more richly fertilized than those containing 

 the pure 0. laeta gametes. The lethal factor of the latter is thus 

 seen to be connected with a smaller degree of attractiveness for 

 the pollen tubes, and this independently of the nature of the latter. 

 Perhaps the amount of attracting substances secreted in the micro- 

 pyle is different in the two cases. 



We now come to the study of the pollen. In crosses with other 

 species 0. laeta and 0. deserens both produce hybrids of the type 

 0. laeta, the brittleness being recessive in the first generation. Empty 

 seeds are not to be expected, and the cultures seem to be wholly 

 uniform during the first months of their development. When the 

 beds are flowering, however, in July and August, two types become 

 visible, although with only small differential characters. One of 

 them is a normal 0. laeta, exactly the same as those from the cor- 

 responding crosses with 0. Lamarckiana. The other has narrower 

 leaves, broader flower buttons, and a weaker stature. It embraces, 

 obviously, the specimens issued from the pollen grains carrying the 

 0. deserens gametes. I made the crosses in the same year as the 

 previous ones, and cultivated sixty flowering offspring of each of 

 them in 1921. The numerical results are given in table II. In this 

 table the second row gives the figures for the hybrids with the 

 normal type of the corresponding 0. laeta as obtained from 0. La- 

 marckiana, whereas the third row embraces those with narrower 

 leaves and broader buttons. 



In group A, the species used for the cross were small flowered 

 ones having small styles. In these no difference between the two 

 types of pollen tubes is shown by the figures. In the large flowered 

 species of group B, however, the difference is very obvious, since 

 the relation is found to be about one-fourth to three-fourths instead 



