328 THE EVOLUTION THEORY 



seems to me to lie in this : that the former has always its basis only 

 in a small majority of the ids of the germ-plasm, while the mutation 

 must be present in most of the ids if it is to be stably transmitted 

 from the very first. How that comes about we cannot tell, but we 

 may suppose that similar influences causing variation within the 

 germ-plasm may bring about variation of many ids in the same 

 direction. I need only recall what I have already said as to the 

 ■origin of saltatory variations, such as the copper-beech and similar 

 cases. The experiments made by De Vries seem to me to give 

 a weighty support to my interpretation of these phenomena. De 

 Vries himself distinguishes a ' pre-mutation period,' just as I have 

 assumed that the variations which spring suddenly into expression have 

 been in course of preparation within the germ -plasm by means of 

 germinal selection for a long time beforehand. At first perhaps only 

 in a few ids, but afterwards in many, a new state of equilibrium of 

 the determinant-system would be established, which would remain 

 invisible until the chance of reducing division and amphimixis gave 

 predominance to a decided majority of the ' mutation-ids.' In the 

 experiments made by De Vries the same seven new 'species' were 

 produced repeatedlj^ and independently of one another in different 

 generations of CEnothera lamarckiuna, and we thus see that the same 

 constellations (states of equilibrium) had developed in many specimens 

 of the parent plant, and that it depended on the proportion in which 

 the ids containing these were represented in the seed whether one or 

 another of the new ' species ' was produced. 



My interpretation, according to which a larger or smaller number 

 of ids were the bearers of the new forms, receives further support 

 from the experiments, for the new species did not always breed true. 

 Thus De Vries found one species, CEnothera scintillans, which only 

 yielded 35-40 per cent, of heirs, or in another group about 70 per 

 cent. ; the other descendants belonged to the forms lamarckiana or 

 oblonga, but the number of pure heirs could be increased by 

 selection ! 



I cannot devote sufficient space to go fully into these very 

 interesting experiments ; but one point must still be referred to : 

 the parent form, CEnothera lamarcJciana, was very variable from the 

 beginning, that is, it exhibited a high degree of fluctuating variability. 

 This tells in favour, on the one hand, of a deep-rooted connexion 

 between ' variation ' and ' mutation,' and, on the other hand, it 

 indicates that saltatory variation may be excited by transference to 

 changed conditions of life— as Darwin in his day supposed, and as 

 I have endeavoured to show in the foregoing discussion. De Vries 



Digitized by Microsoft® 



