1288 BIOLOGICAL EFFECTS OF RADIATION 



polyploid origin — a type of origin undoubtedly characteristic of many 

 angiosperms. Stadler (40a, 44) has discussed the relation of polyploidy 

 to mutation and points out the apparent reduction in induced-mutation 

 frequency and in the frequency of induced partial sterility with an 

 increasing degree of polyploidy in Triticum. On the other hand, just as 

 in A^. Tahaciim, the polyploid character of T. vulgare permits the produc- 

 tion of a large number of chromosomal mutants in the first generation 

 following irradiation (Sapehin, 37). In the same generation many 

 such types are produced in Datura following radium treatment. Thus, 

 of 400 plants, 196 were distinctly abnormal in external morphology 

 (Blakeslee, et al., 6). While all the variants listed in Table 1 are taken to 

 be reflections of induced chromosomal abnormalities, the total number 

 of such alterations in the progenies listed is greater since plants normal 

 in external morphology may, also, possess quantitative changes in the 

 chromosome complement (cf. Bergner, Satina, and Blakeslee, 2). 



In what follows, additional evidence as to induced chromosomal 

 alterations in plants is reviewed in terms of the categories referred to 

 above (page 1281). 



In Nicotiana, 2 tetraploids, 3 triploids, and 11 haploids have appeared 

 in progenies derived from X-radiation or radium treatment of seeds, 

 the growing points of seedlings, or sex cells. Two haploids, one of 

 Tabacum var. purpurea from X-raying of embryos and of one of glutinosa 

 (cf. Goodspeed and Avery, 17) from X-raying of seeds, occurred in X^, 

 while the remainder were found in later generations. Two haploids of 

 glutinosa appeared in Xz from partially fertile, variant X-i plants. Of 6 

 other Tabacum var. purpurea haploids, 2 which occurred in Xz and Xi did 

 not differ significantly from control haploids, while 4 appeared in Xz to 

 Xe progenies of stable derivative types and exhibited their morphological 

 distinctions from control. A haploid plant was, also, found in an A^n 

 progeny of A'^. Tabacum var. Connecticut Broadleaf. The occurrence of 

 none of these haploids, and certainly not those which appeared in X\ 

 after irradiation of embryos or seeds, can be assigned directly to effects of 

 irradiation. In generations after Xi it does, however, appear probable 

 that secondary effects of treatment have played a part in the production 

 of such an apparently high percentage of haploid plants. Thus, the 

 presence of a considerable to a high degree of pollen sterility in the 

 derivative lines may be related to parthenogenetic development of 

 unfertilized eggs under the stimulus of pollen-tube growth and a certain 

 proportion of successful fertilizations. An analogous explanation is 

 given for the origin of haploid plants in Fi interspecific hybrids.^ 



^ In N. glutinosa the only haploids known have appeared in the progenies above 

 referred to. Stadler (43) found a somewhat similar situation in maize, where haploids 

 occurred in cultures of irradiated plants where before they had not been found in 

 untreated lines, but he is likewise doubtful as to the relation of their occurrence to 

 treatment. 



