1/20 HED) caused the most rapid growth, while 

 irradiated barley lagged behind the controls. 



The value of Chekhov's contribution (1930-32) 

 in irradiating various dry and germinating seeds 

 (barley, rye, lentils, and oats) lies in his atten- 

 tion to the condition of the seed at the moment 

 of irradiation, a condition which varies with 

 different times of the year, and even of the 

 month. He demonstrated that weak doses of 

 radiation had a stimulating effect both on germi- 

 nation and on further development. When high 

 doses, which have a depressing effect, were 

 used in experiments with dry seeds, the growth 

 curve does not fall evenly; these doses do not 

 depress germination and the rate of germination, 

 but after germinating a certain percentage of 

 the developing plants dies. As doses are in- 

 creased, the number of plants which die also 

 increases and the onset of death becomes 

 shortened. Very strong doses have the effect 

 that only 1/10 as many irradiated plants germi- 

 nate as compared to control plants. 



Cattel (1931) demonstrated that the growing 

 parts of wheat sprouts are relatively sensitive 

 to X rays. His experiments are remarkable in 

 that he performed them on 200, 000 samples and 

 kept repeating them for a period of 3 years. 

 Dry seeds were thoroughly washed in distilled 

 water; then they were soaked in it for 3 1/2 

 hours and placed in humid chambers; the cham- 

 bers were then placed in thermostats at a 

 temperature of 26° [C]. After 24 hours the 

 coleoptile, leaf, and two lateral rootlets were 

 2 millimeters long; the primary rootlet was 5 

 millimeters in length. At this time sprouts 

 were selected for irradiation (they had to be of 

 equal size and completely healthy). After 

 irradiation the sprouts were once more placed 

 in humid chambers which were set in thermo- 

 stats for 48 hours, after which the sprouts of 

 both the control and irradiated plants were 

 measured. These measurements showed that 

 each of the four growing parts (coleoptile, leaf- 

 lets, lateral and primary rootlets) was affected 

 to a different degree. These changes could be 

 observed after only a few hours. Equal doses 

 of radiation produced equal changes. Sprouts 

 which had received large doses showed various 

 irregularities in their development; rootlets 

 thickened, swellings appeared in cells, etc. 



Shull and Mitchell (1933) set up their experi- 

 ments with extreme care both biologically and 

 physically. Concerning the physical aspect of 

 the experiment, the authors subjected seeds to 

 irradiations which were both quantitatively and 

 qualitatively identical (100 kv, 5 ma, at a dis- 

 tance of 30 cm). Tliey used an aluminum filter 

 1 mm thick. In the biological aspect of the 

 experiment, the authors used seeds of corn, 

 oats, and sunflowers; these were placed in 

 humid chambers on a layer of cotton, soaked in 

 distilled water, and kept at 22° [C]. After 24 

 hours the seeds of all three plants began to 



sprout. Twenty (and sometimes more) seeds on 

 an identical level of development were selected, 

 whenever possible, and were divided into two 

 parts. One part was retained for control, and 

 the other was placed on fresh damp cotton and 

 irradiated. The optimum irradiation for sun- 

 flowers turned out to be 3 minutes (i. e. , 144 r); 

 for corn and certain varieties of wheat, the 

 optimum dose was 2 minutes. For other vari- 

 eties [of wheat] exposures of 30, 45, or 60 

 seconds were sufficient. As soon as the irradi- 

 ations were concluded, the irradiated seeds 

 and controls were planted in soil, sand, or on 

 cotton in the humid chamber. Experiments 

 demonstrated that a variety of hard wheat, 

 "Minhardi, " was less sensitive to X rays than 

 "Trumball" which in turn was less sensitive 

 than a variety known as "Marquis. " From this 

 the authors concluded that just as there exist 

 varieties which are more resistant to cold, 

 there are those which are more resistant to 

 radiation. The most interesting data were 

 obtained with corn, a variety called "Madison 

 Yellow Dent. " Turgid kernels of corn were 

 divided into three parts: the first was irradiated 

 with an aluminum filter, the second without one, 

 and the third part was used as a control. Deter- 

 minations of moist and dry weight of the coleop- 

 tiles showed that irradiated seeds are from 5 

 to 26% heavier in the moist and from 3 to 16% 

 heavier in a desiccated condition. It is possi- 

 ble to ascribe this increase in weight of the 

 coleoptiles to a faster utilization of the endo- 

 sperm reserves of the irradiated seeds. Sev- 

 eral weeks after irradiation the plants receiving 

 1- to 3-minute doses had thicker stems than the 

 controls or those receiving 5-minute doses. 

 The weight of the green part of the plant was 

 greater in the irradiated plants. 



Oats [when irradiated] grew irregularly but 

 at a noticeably rapid rate. A comparison of 

 the controls and irradiated seeds of sunflowers 

 gave a good curve for their development. A 

 group of plants that had been irradiated for 3 

 minutes was the first to blossom. These ex- 

 periments indicate that when experiments are 

 carefully set up, and the proper dosages are 

 used, favorable results can be obtained. Un- 

 fortunately, the authors did not follow through 

 their experiments until the crops were harvested 

 nor did they repeat their experiments. 



Benedict and Kersten [1934] used rays which 

 were practically monochromatic. They placed 

 grains of wheat in special dishes such that all 

 the buds pointed in the direction of the [X-ray] 

 tube at a distance of 1 centimeter from the 

 aperture and that a lead shutter could be in- 

 serted between the seeds and the aperture. 

 After irradiation, the seeds were treated with 

 fungicide and allowed to sprout; then their 

 diastatic activity, content of reduced sugar, 

 respiration, and water content were deter- 

 mined. Sprouts exposed to radiation for 5 sec- 

 onds showed an increase in diastatic activity 



11 



