THE MUTATED GENE 153 



increase without impairing the vigor of the plant. The position 



of this optimum differs in different cases. It would be difficult 

 to draw direct conclusions upon genie action from such fads. 



There are, in addition, numerous physiological effects of 

 polyploidy, which, in part at least, may be directly caused by the 

 change in cell size. But it is questionable whether all effects 

 may be caused in such a way. From the long list of facts that 

 Muentzing has compiled from botanical literature it follows that 

 most quantitative traits are influenced; e.g., the growth curve 

 and the time of flowering are retarded. According to Wettstein 

 and his students, this is a consequence of a change in rate of cell 

 divisions. In other cases, the osmotic conditions are changed; 

 the starch or vitamin content is increased; resistance to cold is 

 heightened; general metabolism and chemical composition are 

 changed. The few cases in animals (Artemia salina, according 

 to Artom, 1920, 1926; Gross, 1932; psychid moths, Seiler, 1927) 

 seem to show parallel traits. Most of the authors agree that all 

 these effects are in the end caused by the change of cell size. If 

 this is the case, the physiological facts do not lead further than 

 the morphological ones, in so far as our problem is concerned. 



But there is a more indirect way in which the study of poly- 

 ploids has contributed to the knowledge of the action of the gene. 

 In his extensive experiments on polyploidy in mosses, Wettstein 

 (1924b) found that in pure races the experimentally produced 

 polyploids show a simple geometric increase of cell volume w r ith 

 chromosome number up to the possible limit of about 4n. This 

 limit, in regard to addition of more chromosome sets, may, 

 however, be shifted considerably if hybrids are used for the 

 experiments. In this case, up to 16 chromosome sets could be 

 attained. This is possible because in such hybrids the increase 

 in cell size is regulated so that the additional growth is no longer 

 proportional to the chromosome number but decreases with 

 further addition of genoms. This regulation of cell size occurs 

 according to a definite curve (Fig. 31) which reaches its maximum 

 asymptotically. The equation of this curve is identical with the 

 equation of a monomolecular reaction. Wettstein had formerly 

 shown that genes exist in the pure species that control the basic 

 cell volume as well as the proportionality factor for its geometrical 

 increase with chromosome number and that these genes differ 

 in both species involved (Funaria, Physcomit rella) . He assumes, 



