1286 



BIOLOGICAL EFFECTS OF RADIATION 



shows such extreme and apparently complete disruption of chromosomal 

 mechanisms in mitosis and meiosis that gametic or zygotic lethality 

 leading to complete sterility might be anticipated. This was, in general, 

 the result obtained, but in some cases a small amount of seed was pro- 

 duced, giving progenies which in external morphology, genetic behavior, 

 and chromosomal constitution (Goodspeed, 136) showed the extent 

 to which nuclear alteration in this species can go without consequent 

 inviability. Thus, in one instance in which the chromosomes of PMC 

 were seen to have been very severely disrupted following heavy X-ray 



Fig. 4. — Flowers of A'. Tabacum var. purpurea, (a) Control, (6), (c), and (d), types 

 obtained in third generation after X-radiation from a "normal" in the first generation 

 progeny, the extent of variation in which is shown in Fig. 3. 



dosage (Fig. 2), a small set of viable seed was obtained on self-pollination 

 and in a progeny of 48 plants grown from it (Table 1, fourth case), only 

 two approximated the control while many showed extreme variations 

 in all vegetative and floral characters. Figure 3 gives evidence of the 

 alterations in flower size, form, and color, which occurred. A progeny 

 grown from one of the two plants apparently normal in external mor- 

 phology again showed a large range of variants and from certain of these 

 it has been possible to establish distinct derivative types (Fig. 46, c). 

 In other plant species, also, a similar amount of variation following 

 irradiation has been observed and undoubtedly is in large part a reflection 

 of various sorts of induced chromosomal alteration (cf. Lindstrom, 28; 

 McKay and Goodspeed, 31; Horlacher and Killough, 22). 



