THE MUTATION THEORY in 



the parental combinations are in excess. This excess almost 

 certainly follows the system indicated by the accompanying 

 table. In the general expressions n is half the number of gametes 

 required to express the whole system. Now if we imagine that 

 sex-factors are involved with the others concerned in such a re- 

 lationship as this we have a system of distribution approximating 

 to that found in biennis and muricata. The difference in re- 

 ciprocals is represented in a not improbable way. It cannot yet 

 be said that the rarer terms in the series are formed at all, and 

 perhaps they are not. As we pointed out in our discussion of 

 these phenomena, the peculiar distribution of factors in these 

 cases must be taken to mean that the planes of division at some 

 critical stage in the segregation are determined with reference 

 to the parental groups of factors, or in other words, that the 

 whole system has a polarity, and that the distribution of factors 

 with reference to this polarity differs according to the grouping 

 of factors in the gametes which united in fertilization to produce 

 the plant. Subsequent proliferation of cells representing certain 

 combinations would then lead to excess of the gametes bearing 

 them. It is on similar lines that I anticipate we shall hereafter 

 find the interpretation of the curious facts discovered by de Vries, 

 though it is evident that a long course of experiment and analysis 

 must be carried through before any certainty is reached. The 

 work must be begun by a careful study of the descent of some 

 single factor, for example, that causing the broader leaf of 

 biennis, and we may hope that the study of Oenothera by proper 

 analytical methods will no longer be deferred. 



We have now to return to the relations of laeta and velutina. 

 These two forms, it will be remembered are frequently produced 

 when Lamarckiana or one of its derivatives is used as male, 

 and the most unexpected feature in their behaviour is that both 

 breed true as regards their essential characteristics, on self -fertili- 

 sation. If one only bred true the case might, in view of the 

 approximate numerical equality of the two types, be difficult 

 to interpret on ordinary lines, but as both breed true it must be 

 clear that some quite special system of segregation is at work. 

 What this may be cannot be detected on the evidence, but with 



