78 Mutations and Evolution. 



heredity and variation, have had a wide vogue in recent years. On 

 the other hand, Loeb (1916) and from a different point of view, 

 Ritter (1919), among others, have recently championed the 

 organism-as-a-whole. The latter writer has pressed this view 

 farthest, in the endeavour to eliminate elementalist conceptions 

 altogether. We believe a truer attitude lies in the recognition of a 

 fundamental truth in both these aspects. 



In a former work 1 and in earlier chapters of this series we 

 developed a cell theory of mutations emphasizing the fact that each 

 new form arises as a germinal difference from the parent type. The 

 cell unit, in all such variations, is the thing which has changed, and 

 the new external characters which appear in every part of the 

 organism are the structural result of an ontogeny built up with 

 a different unit as basis. 2 This situation was particularly clear in 

 (Enothera gigas, where it was shown 3 that the volume of the nuclei 

 and cells has increased in varying proportions in different tissues. 

 Tupper and Bartlett (1916) have confirmed and extended these 

 results in the case of (E. stenomeres mut. gigas which is also tetra- 

 ploid or 4.v in the constitution of its nuclei. 



Without going farther afield for confirmatory data, which are 

 amply furnished in the contemporary literature, we may conclude 

 that the mutation theory of germinal variations is firmly grounded 

 upon the cell theory, and if the cell theory were universal in its 

 application then mutations or germinal changes might be supposed 

 to supply the whole of the material for evolution in organisms. 

 Pacts such as those pointed out above lead to the concept of the 

 species cell. This is a conception which has been independently 

 arrived at by different lines of approach (see, for example, Lang, 

 1909). It is a sounder and less extreme conception than that of the 

 organism as a cell-state, i.e., merely an aggregation of more or less 

 independent cell units. 



Biologists have long recognized the necessity for limitations of 

 the cell theory of organic structure. On the one hand we have the 

 legitimate and necessary conception of the species cell, briefly set 

 1 The Mutation Factor in Evolution. 



1 If this be the case, then the mitoses during ontogeny do not bring about 

 the unequal division and sorting out of portions of the chromosomes, as 

 Weismann supposed ; but all these divisions are, as they appear, equational 

 so far as the chromosomes are concerned. This conclusion has also been 

 reached from the study of experimental embryology (Conklin, 1916) and from 

 other lines of approach. So far as the chromosomes are concerned, their 

 materials are apparently not as a rule segregated by differential divisions 

 during ontogeny. On the other hand, differential divisions of the cytoplasm 

 are of frequent occurrence. 



Gates, 1909a, 



