1282 



BIOLOGICAL EFFECTS OF RADIATION 



may, as indicated, be directly induced or may arise as a result of gene 

 mutation (asynapsis) or as a by-product of chromosomal reorganization, 

 while monosomy and polysomy may themselves give triploidy. The 

 dotted lines indicate that polyploidy and extreme nuclear disruption 

 may possibly be secondary products of induced gene mutation. Thus, 

 Stein (456, 466, 47) interprets her "phytocarcinome complex," which is 

 characterized by these effects, as due to an induced mutation. Chro- 

 mosomal reorganizations are indicated as the direct consequences of 

 irradiation and may give rise in subsequent generations to haploidy, 

 triploidy, and tetraploidy. In addition they are shown as a mode of 



origin of gene mutations, a significant 

 type of effect from the point of view 

 of the origin of mutation. 



In this connection the results of 

 Stubbe (48) are significant. Using 

 mature pollen of Antirrhinum majus, 

 he compared mutation frequency 

 after treatment with grenz (supersoft) 

 rays and longer and shorter X-rays, 

 the dosage in each case increasing 

 in geometrical progression. That the 

 curves obtained from the three 

 treatments are directly comparable 

 is interesting in other connections, 

 but their present significance lies in 

 their consistent and decided fall from 

 a rapidly attained peak, followed by 

 their rise. As to the nature of the 

 mutations themselves, those responsible for the initial rise in the 

 curve were similar or equivalent to those which had been observed 

 in Antirrhinum under natural conditions. Stubbe's results may be 

 interpreted as indicating that a series of qualitative (intragenic, 

 chemical) changes were initially induced, followed by quantitative 

 (extragenic, chromosomal) alterations productive of lethality and 

 giving by-products of such extragenic alteration which behaved 

 genetically as did the gene mutations first produced. Although Stubbe 

 assigns all the mutations, which were identified without cytological study, 

 to induced transgenation ("labile" vs. "stable" gene mutations), he 

 recognizes that quantitative chromosomal alteration may, in part at least, 

 have been responsible for their occurrence. 



That structural alterations in plant chromosomes are readily induced 

 by high-frequency radiation has long been recognized and the alterations 

 themselves have been frequently described (cf. Koernicke, 24; Levine, 25; 

 Pekarek, 35; Timcf^eff-Ressovsky, 49). Chromosomal "fragmentation" 



Fig. l.^Chart illustrating primary 

 and secondary effects of high-frequency 

 radiation in inducing chromosomal altera- 

 tions in plants. 



