974 BIOLOGICAL EFFECTS OF RADIATION 



fused with the main rachis so that no petiole was present or the tip edge of 

 the leaflet was attached to form cuplike structures. 



Rivera (53) found that irradiation of the castor bean caused retarda- 

 tion in the development of the shoot. Subsequent growth showed poorly- 

 developed leaves with very irregular margins. 



Sprague and Lenz (62) , who irradiated sprouted potato tubers, noted 

 the peculiar shape of the first leaves. The tips appeared injured and the 

 blade seemed to be pinched in. Leaf margins curled downward and 

 the leaf in general appeared more glossy than normal leaves. Later the 

 leaves became normal. 



Navashin (46) found that seedlings from soaked seeds of Crepis 

 tectorum showed marked influence of X-rays as early as six days after 

 germination. Delayed and abnormal development of the first leaves 

 seemed clearly connected with the dosage employed. Johnson (20) 

 found that the cotyledons were little affected by radiation. However, 

 irregularities in number and size of cotyledons as well as anomalies in 

 leaf shape were evident in cotton seedlings irradiated by Horlacher and 

 Killough (16). Numerous irregularities in leaf color, including a sectorial 

 chimera, were noted. 



Development of axillary buds following irradiation was reported by 

 Ancel (3a) who exposed growing tip cells to the rays but protected roots 

 by a layer of leaded caoutchouc. Growth activity was transferred to 

 the axillary buds. 



Rivera (54) wrote of "buds of restitution" which follow the initial 

 arrest of development. He reported the accelerated development as 

 stimulation, and believed that he had found doses which stimulated 

 development of the aerial parts as well as the roots. 



Excessive branching of stems of irradiated seedlings and stem fascia- 

 tion have been described by Johnson (19, 21) for species of Helianthus 

 and Ly coper sicon. In fact, many ray-susceptible plants showed this 

 character after treatment. Stems showed fasciation three weeks after 

 irradiation; they were generally cylindrical at the base, but the apex 

 was diffusely branched. The stems after becoming flattened usually 

 showed splittings somewhere along their lengths; the resulting branches 

 sometimes remained unfasciated, but in many cases they themselves 

 became divided again. Grooves appeared in portions of the stem. 

 Dichotomous branching often occurred in the sunflower 50 to 90 cm. 

 from the stem base; further splitting of the stem occurred with six or 

 more tips becoming evident. The percentage of fasciated stems increased 

 with an increase of dosage given to young seedlings. 



Tomato plants receiving medium dosage of X-rays developed many 

 lateral branches which caused them to assume a bushy appearance. 

 Increase in branch development was found to be from 27 to 65 per cent 

 greater in the irradiated plants than in the controls. Other plants which 



