152 PHYSIOLOGICAL GENETICS 



The genic-balance-theory, in the form used by Bridges, 

 expresses these effects as follows. The plus and minus modifiers, 

 the balance of which determines for each character its condition 

 in the Wild type, are distributed at random along the chromo- 

 somes. It' one chromosome is removed, it will usually happen 

 that more plus than minus modifiers (or vice versa) for one or for 

 several characters will be removed. Consequently, more of the 

 other type will be lefl in action, and the character will be shifted 

 in that direction. Apparently, not much meaning can be 

 attached to this form of description as far as the action of genes 

 in controlling developmental processes is concerned. It seems 

 advisable, therefore, to discard the term genie balance in favor of 

 balance of gene-controlled reaction velocities. 



A special problem of dosage effect is presented when whole 

 chromosome sets are involved in polyploidy, and therefore the 

 dosage of all genes is increased concomitantly. What may be 

 changed in this case is (1) the proper relation of gene action (if 

 proportional to dosage) to the cytoplasmic substratum. (2) 

 The threshold for the maximum effect of gene doses may be 

 different for different genes; therefore at a higher dosage some 

 may increase their effect proportionally, others not (when their 

 threshold is reached). This, again, would result in a disharmony 

 in the time of the reactions. The effects of polyploidy might 

 therefore also be used to a certain extent in analyzing genie action. 

 It is generally known that polyploids might be more or less differ- 

 ent from the diploids. Muentzing (1936) has recently reviewed 

 all the known cases and compiled an extensive table showing the 

 effects of abnormal number of chromosomes in natural chromo- 

 some races of plants. He states that hardly any cases are known 

 in which no differential features from the normal diploid could be 

 found. He t hen compares the natural polyploids with the experi- 

 mental ones and comes to the conclusion that the effects are the 

 same. It is generally known that these effects are mostly 

 quantitative in regard to all parts of the plant, producing the 

 gigas type, though the details may vary in different cases. It 

 is generally assumed that these differences are the result of the 

 increase in cell size as a consequence of the existence of the 

 karyoplasmic ratio, making cell size proportional to chromosome 

 number. But there are also exceptions due to the fact that there 

 is an optimum beyond which chromosome number may not 



