VARIATION. 39 



Numerous instances of discontinuous variation, resulting 

 from a variation in the action of non-inherited factors of the 

 development may be gathered. A beautiful example is the case 

 of the twisted teazels reported by de Vries. 



De Vries grew a strain of teazels, Dipsacus, which differed 

 from the normal in their remarkable response to abundant 

 nourishment. All the well-nourished, strong rozettes of this 

 strain grow up into twisted individuals. All the weaker rozettes 

 grow up normal. Intermediates are absent. That the difference 

 is not dependent upon any difference in inheritable constitu- 

 tion, is shown by the fact that sowings of the seed of normal as 

 well as of seed from twisted individuals always give the same 

 mixture of normal and twisted plants, the relation between 

 the two kinds being again decided by more or less nourish- 

 ment. A great number of cases of "ever-sporting varieties" fall 

 into this class, though obviously some of the cases of ever-spor- 

 ting variability given by de Vries are fundamentally different, 

 and are to be explained as rather complicated cases of segre- 

 gation of inherited factors. 



If we could study the influence of the different development- 

 al factors of both types in an ideal way, so that all other fact- 

 ors could be kept constant, we would nearly always see, that 

 the non-inherited developmental factors itself vary continu- 

 ously, and that the resulting organisms would vary contin- 

 uously in a corresponding way. And in the study of inherited 

 factors, which as we know, cannot vary in intensity, but are 

 either present or absent, we would see a discontinuous vari- 

 ation. We would always be able to distinguish those individuals, 

 which had developed under the influence of our factor, from 

 those to whose developement it had not cooperated. But of 

 course in reality all the qualities of an organism are influenced 

 each by so many different factors, which may vary indepen- 

 dently, and in different ways, that the influence of the less 

 important factors on the qualities of the organisms may be 

 wholly obscured. 



If we sow part of a homogeneous lot of seeds in a dry sterile 



