LEE BARKER WALTON 153 



and others, than one based on the mutational idea, and 

 it is to fossil forms that one must look for the all-impor- 

 tant historical record. 



Should one propose a hypothesis of an ultimate unit, 

 slightly plastic as to its immediate environment, but sub- 

 ject to the permutations and combinations of a mendelian 

 type, and possessing a definite qualitative condition de- 

 termined by prolonged environmental action, the picture 

 is not at all so fanciful as some might at first thought 

 insist. 



The practical importance of such a viewpoint in its 

 application to the problems of animal and plant breeding 

 lies in the realization that new forms can not be created, 

 but merely new combinations uncovered during the com- 

 paratively brief epochs of time which human intelligence 

 has for working out the processes. Thus one returns to 

 genetics. 



In summarizing the paper, the following conclusions 

 are suggested: 



I. The heritable characters in general which make up 

 an organism arise from preformed units in the nature of 

 genes or subgenes that have been in existence during long 

 geological periods of time. There are at present no cri- 

 teria available in modern genetics by which an apparently 

 new gene may be distinguished from one long in existence; 

 furthermore, there is doubt as to whether new genes are 

 actually arising in multicellular organisms. The change 

 of a gene in a given direction, whether it be considered as 

 a morphological unit or a chemical condition followed by 

 the return to its original condition, suggests its composi- 

 tion of combinational sub-units, and is an argument 

 against the idea that anything actually new has come into 

 being during its series of so-called mutations. Such a 

 conclusion receives additional support from the presence 

 of apparently identical genes which exist in distinct species 

 of organisms separated during long epochs of time, as well 

 as from the evidence of the non-contamination of genes 

 during diverse environments. 



II. The mutations demonstrated by DeVries and oth- 

 ers, together with the variations obtained by Castle, are 



