250 Hybrids breeding true [CH. 



de Vries mentions some cases which he accepts as satis- 

 factory, the most definite being that of Oenothera muricata 

 x biennis raised by himself. The hybrids were partially 

 sterile in a high degree, but the subsequent generations 

 raised from them showed no definite departure from the F^ 

 type. The evidence, as it stands, must be taken as consti- 

 tuting a definite exception. Nevertheless in view of the 

 great sterility exhibited by the hybrids, and the fact that 

 all that we know of the Oenothera crosses points to the 

 existence of very unusual features in their genetic physio- 

 logy, the significance of this curious observation is still 

 somewhat problematical* 



Another case given by de Vries is that of Anemone 

 silvestris x magellanica on the authority of Janczewskif- 

 As this case well illustrates the anomalous and uncertain 

 behaviour of partially sterile hybrids, the facts are worth 

 giving in some detail. In the first account the hybrids are 

 said to have been either totally sterile, or fertile in a very 

 slight degree. The pollen is said to have been all bad, 

 and in flowers containing about 100 pistils, one or rarely 

 two good akenes formed. Janczewski thinks that these 

 were fertilised from one of the parents. But the hybrid 

 sometimes gave rise by an adventitious bud, from the root, 

 to a plant having the female parts perfectly fertile, pro- 

 ducing akenes of intermediate shape. The pollen of these 

 flowers was not examined, and it was supposed that fertilisa- 

 tion was effected by pollen of A. sylvestris growing near by 



In the later account it is recalled that the hybrids some- 

 times produced good akenes among a multitude of abortive 

 ones, and it is said that the pollen, though very bad, contained 

 occasional good grains which could effect fertilisation without 

 foreign pollen. Some stems of this hybrid not the whole 

 plant gave rise suddenly to flowers perfectly fertile, with 

 all the akenes good. These flowers had mixed pollen-grains, 

 of which about three-fourths were good and effected self- 

 fertilisation. The second and also the third generations 

 raised from the hybrid, whether from the sterile or from the 

 fertile flowers, reproduced precisely the characters of the 

 original hybrid, exhibiting the complete fertility of the female 



* See Appendix to Part I. 



t Bull. Ac. Cracovie, 1889, June, No. 6, p. xxiv, and ibid. 1892, p. 228. 



