With a dose of 750 r it increased by 30%, the 

 size gradually diminishing as the dosage in- 

 creased. Analysis of the yield indicates that 

 the number of ears increases nearly three times, 

 as do the number and weight of seeds per plant. 

 The advantages of irradiation are not limited to 

 an increase in yield of the directly irradiated 

 plant; they are also transmitted to the descend- 

 ants of the irradiated plant. Seeds collected 

 from irradiated plants gave an increased yield 

 the following year. With a dose of 750 r the 

 increase was 37. 99%. 



Since pea seeds are known to be extremely 

 radiosensitive, the weakest possible doses of 

 X rays were used for their irradiation. In the 

 first experiment the number of pods per plant 

 doubled (in comparison with the controls) when 

 a dose of 450 r was used. In an experiment of 

 another year a dose of 350 r raised the weight 

 of seeds per plant from 3. 66 grams (weight of 

 the control) to 5. 07 grams. 



Irradiation of the seeds and sprouts of spring 

 wheat produced neither stimulation of develop- 

 ment nor increase in yield. Only high doses of 

 X rays (8000 and 16, 000 r) clearly exerted a 

 depressing effect. 



Summarizing our 5 years of experiments 

 with three [kinds of] plants, we can draw the 

 conclusion that exposure of rye and peas to 

 X rays before planting causes stimulation of 

 their development and increase in yield. For 

 wheat, we have so far been unsuccessful in 

 finding doses that produce either of these above 

 results. 



Rye Grass (investigations of Breslavets) . 

 Several years had passed since the end of our 

 experiments concerning the effect of X rays on 

 agricultural crops, when the question of appli- 

 cation of these rays to meadow grasses came 



up. One of these was the Vesterval'd rye 

 grass, picked out as the most rapidly growing 

 one. Doses of 200, 300, 400, 500, 750, 1000, 

 2000, 4000, and 8000 r were selected for these 

 plants as well as controls. They were planted 

 on February 24, 1942, in quadruplicate. First 

 the time of germination of seeds with the vari- 

 ous dosages was noted (Table 12). 



These data show that doses of 300, 400, 500, 

 and 2000 r cause all seeds to germinate, while 

 in the controls only 76% germinated. We have 

 come across this type of phenomenon more than 

 once in our experiments with X rays on the 

 seeds of many other species of plants. These 

 facts should be noted since they show that 

 valuable seeding material can be saved by the 

 use of radiation. 



By the end of March the plants had developed 

 to such a point that it was no longer possible to 

 leave them in boxes. They were removed from 

 the ground and the number of roots on each plant 

 for each dosage was counted. In addition, the 

 lengths of roots and stems, and the weight of 

 the stems were recorded (Table 13). 



As can be seen from Table 13, a dose of 

 750 r nearly tripled the number of roots, in- 

 creased the length of stems by 19%, the length 

 of the roots by 25%, and the weight of the stems 

 by 76%. The above dose obviously stimulates 

 the growth of the plants, while a dose of 8000 r 

 which depresses plant development can be used 

 to create the impression of unevenness in the 

 soil due to the uneven development of the plants. 



For the number of roots we can see the 



typical biological curve of the Arndt-Schultze 



Law: a gradual rise up to and including 750 r 



and then a gradual falling off to the dose of 



! 8000 r. The same may be observed for length 



I of stems and roots, and weight of stems. From 



Table 12 



[Percentage of seeds which germinated at 4 successive dates after various X-ray doses] 



(based on Breslavets' data, 1942*) 



^This figure should be 100 according to the statement below the table. 



26 



