262 Fertilisation and Hybridisation 



stable. The given individuals overstep their bounds, 

 abandon the earlier type, and form a new species. 



It is evident that in crossings such unstable units will 

 behave differently from normal, stable ones. Their 

 chance of becoming stable is evidently considerable, ow- 

 ing to the phenomena of fertilization and the exchange of 

 units. In this way constant races originate, at least in the 

 genus Oenothera, and this, on the one hand, with the re- 

 spective characteristic in an unstable condition, or in other 

 words, in a state of mutability ; and on the other hand with 

 stable equilibrium corresponding to a new species. But 

 researches in this field are only in their beginning, and do 

 not yet permit of a detailed analysis. Besides they repre- 

 sent, for the present, a case in themselves. 



* * * 



In conclusion, on reviewing the course of our deduc- 

 tions, we see that hybrids follow normal fertilization quite 

 closely, the more completely the less numerous and the less 

 pronounced the points of difference between the parents 

 of the crossing. If these are of such a kind that the num- 

 ber of units in one parent is different from that in the 

 other, disturbances take place which, if of lesser influence, 

 diminish the fertility of the hybrids, and if of greater sig- 

 nificance, affect their own power of development, or even 

 'make the crossing a failure. If these units are present 

 in equal numbers on both sides, and if the differences are 

 limited to latency in one parent and activity in the other, 

 the normal process is not at all disturbed, but striking 

 phenomena occur, which find their explanation in the pe- 

 culiar manner in which the parental inheritances co-oper- 

 ate in the hybrid and in the formation of its sexual cells. 

 This co-operation is reflected in the life of the nuclei. 



