THE LAW OF JOHANNSEN. 223 



thinks that selection-experiments with clones of uni-cellular 

 creatures bear upon the problem of the purity of pure lines, 

 shows, that he sees the point of the discussion in something 

 different from what we consider essential. To our mind, the 

 purity or otherwise, of clones and pure lines alike, is non-essen- 

 tial as compared to the qualitative purity or otherwise of the 

 genes. 



This is the real problem with which we are concerned. Are 

 the genes really qualitatively stable? Have we to explain this 

 purity of groups of individuals which originate out of repeated 

 self-fertilizations, under all sorts of conditions, even selection, 

 as due to a qualitative stability of the genes for which they 

 are homozygous? 



And if we state the problem in this way, some facts become 

 very significant. In the first place we saw that no instances 

 have been adduced, which show the effect of selection in mul- 

 ti-cellular organisms in material which we have good reason to 

 believe to be pure and homozygous. We are now leaving on one 

 side Castle's example, as Castle has recently stated his con- 

 conversion to a belief in the stability of the genes. 



In the second place, we know that selection within clones of 

 higher plants like sugar-cane and dandelion and beets and 

 potatoes is ineffective with some significant exceptions, namely 

 with the exception of the occasional quasi-spontaneous 

 production of novelties. We know, that these novelties arise 

 in some clones independently of selection, and if they occur 

 during a selection, are more often in quite irrelevant direct- 

 ions than not. 



We further know from Salaman's work that such novelties 

 produced by clones, are the same novelties the plants will 

 produce by self-fertilization. In other words, these cases can 

 be explained by somatic segregation, and they have nothing 

 to do with qualitative changes in genes. We further know 

 how in graft-hybrids disturbances in the arrangement of the 

 genetically different cell-layers are often noticed, within the 

 individual as well as during asexual multiplication. The work 



