the frequency of spontaneous mutations, but 

 also the action of short waves that induce muta- 

 tions. However, the mechanism of the action 

 upon which this fact is based is completely un- 

 known. Since up to now [Doring and] Stubbe 

 (1938) have investigated the absence of those 

 elements (nitrogen, phosphorus, and sulphur) 

 which enter the composition of the chromo- 

 somes, it is understandable that disruption in the 

 metabolic function of these elements leads to 

 irregularities in the structure of the substance 

 of the genes, i.e., to mutations. A calcium 

 deficiency does not increase the percentage of 

 mutations, but then calcium is not an essential 

 part of the substance of the gene. 



Stadler (1929) adopts an extremely interesting 

 point of view in explaining the diversity of the 

 effects of X rays on various species and genera 

 of plants. He established that different species 

 of the same genus manifest differences in their 

 ability to undergo mutations. The irradiation 

 of seeds of Avena sativa, A. bysantina , A. 

 strigosa, Triticum monococcum, T. dicoccum , 

 T. durum, and T. vulgare with identical doses 

 leads to different results. Whereas the species 



A. brevis and A. strigosa show increases in 

 the percentage~bf mutations when subjected to 

 irradiation, A. bysantina and A. sativa do not 

 react at all in this respect. Similarly in T. 

 monococcum, the percentage of mutations is 

 very great and it falls gradually through dicoc- 

 cum and durum to vulgarum , which doesnT 

 exhibit any mutations (Table 38). 



By comparing the data of this table we see 

 that the frequency of observable mutations de- 

 creases as the number of chromosomes in- 

 creases. By way of explanation Stadler offers 

 the following hypothesis. If we assume that in 

 A. bysantina and A. sativa the same gene is 

 present in each genome in a dominant condition, 

 then the formula for this genome will be 



A ^ Ag A; 



A J Ag A3 



If a mutation occurs from A to a. 



it will lead to a heterozygous condition 



AAA 



^ "^ "3 ' which in time will lead to a homo- 

 a 1 A2 A3 



zygous condition 



Ao Aq 



■ This plant will not 

 a I A2 A3 



show any change since the four dominant allelo- 

 morphs will mask the two that have undergone 



Table 37 



Combined Tables. Experiments with Anitrrhinum majus L . 

 (based on [Doring and] Stubbe' s data, 1938) 



Type of Action 



Full diet (unirradiated) 



Phosphorus deficiency (unirradiated) 



Full diet (4^,000 r) 



Phosphorus deficiency (4-6, 000 r) 



Cultures 



498 

 587 

 543 

 966 



Number of 

 Mutations 



44 

 118 



Mutations in each 

 100 [Fg] Plants 



1.004 + 0.44 



1.362 j- 0.47 



7.099 + 1.10 



11.211 -f 1.01 



Table 38 



Frequency of mutations obtained by experimental means 

 in various species of Avena and Triticum . 

 (based on Stadler' s data, 1929) 



106 



