difference: the plants exposed to X rays re- 

 ceived full color more slowly than the plants 

 which had not been subjected to radiation. This 

 observation forced Atkinson to assume that X 

 rays exert a certain detrimental effect on plas- 

 tids. He did not succeed in establishing any 

 other differences in the plants despite the pro- 

 longed exposure. 



Lopriore in his experiments (1897) found 

 indications of the stimulating effect of X rays. 

 By subjecting parts of plants of Vallisneria 

 spiralis to X rays, an acceleration of the move- 

 ment of protoplasm in the cells was discovered. 

 By subjecting germinating pollen tubes of two 

 plants ( Genista and Darlingtonia ) to the action 

 of X rays, he succeeded in slowing down the 

 process of germination. 



Maldiney and Thouvenin (1898) were the first 

 to perform experiments involving irradiation of 

 seeds (they used seeds of Convolvulvus arvensis , 

 Lepidium sativum , and Panicum miliaceum) ; and 

 concluded that X rays accelerate the germination 

 of seeds. In addition, they observed that X rays 

 do not affect the formation of chlorophyll since 

 the sprouts come up from the ground with the 

 characteristic pale green coloring. Unfortu- 

 nately, the amount of seeds used (only 3 in each 

 experiment and in each control) was not signifi- 

 cant. The question of stimulation by exposure 

 to X rays consequently remained unsettled as a 

 result of insufficient evidence. However, as 

 compared with previous experiments, this is a 

 step forward since the authors noted the amper- 

 age and the distance from the source of radia- 

 tion. 



Perthes* (1904) studied the effects of X rays 

 on Vicia faba seeds which have since become the 

 favorite subject for experiments with radiation. 

 By measuring the length of roots in exposed and 

 control plants he established the retardation of 

 growth in irradiated plants. His experiments 

 thus demonstrated the inhibiting effect of X rays. 

 As a counterpoise to this, the experiments of 

 Evler (1906) showed that the irradiated seeds of 

 beans, radishes, lettuce, squash, and cucum- 

 bers exhibited greater energy in sprouting, 

 more powerful development, and earlier bloom 

 than the control plants. 



In his first comprehensive experiments, 

 Kornicke (1904, 1905) used the seeds of Vicia 

 faba , Vicia sativa , and Brassica napus in large 

 numbers. His experiments were distinguished 

 by being more thoroughly set up and controlled 

 than those of his predecessors. First he investi- 

 gated the effects of radiation on seeds in various 

 states: dry, turgid, and germinating. Secondly, 

 the X rays were used in definite, and ever in- 

 creasing dosages expressed in Holtzknecht units 

 (H), in the following quantities: 16, 20, and 26. 

 With small dosages Kornicke observed tempo- 

 rary arrest of growth; with higher doses, total 

 cessation of growth. In the following experiments 



a dosage of 20 H produced a small acceleration 

 in Vicia faba and a significant one in Brassica 

 napus . The difference between the irradiated 

 plants and the controls was striking; from 100 

 irradiated seeds of Brassica napus 50 germi- 

 nated; from the same number of control seeds, 

 only one germinated. In due time, however, the 

 differences between the irradiated and control 

 plants disappeared entirely. 



Guilleminot (1907) used seeds of the gilly- 

 flower (Mathiola) in batches of 20 for his experi- 

 ments. Sixteen batches were subjected to pro- 

 portionately increasing dosages of X rays from 

 10 to 20, 000 r. Sixteen other batches received 

 various exposures to radium and four were 

 retained for control. Two control batches were 

 left under normal conditions, one at maximum 

 dryness, and the last batch under increased 

 humidity. From these experiments he concluded 

 that retardation of growth is characteristic for 

 irradiated plants, provided the dosage is suffi- 

 ciently great. Acceleration of growth was ob- 

 served when the plants were exposed to dosages 

 of between 5000 and 7500 r, but the results were 

 too small to be significant. 



By the time Schmidt began experiments in 

 1910 it had become customary to express dosages 

 of radiation in HED [Skin Erythema Dose]. Peas 

 that had previously been soaked in water for 6 

 hours were exposed to various doses of X rays 

 (1/20, 1/10, 1/4, 1/2, and 1 HED). The plants 

 raised from the irradiated plants possessed 

 unusual size (45 to 50 cm); their leaves and pods 

 were twice the size of unirradiated plants, and 

 contained from four to five peas per pod, while 

 normal plants contained only two or three. The 

 experiments led to the following conclusion: 

 "It appears to me most probable that this fact 

 should have practical significance for horti- 

 culture and pomology. " TTius, Schmidt con- 

 firmed the existence of stimulating doses, while 

 the experiments of Wetterer [1912 - 1913] re- 

 sulted in diametrically opposite conclusions. 

 A group of turgid sunflower seeds was divided 

 into five equal parts. The first part was re- 

 tained for control, the second received 5 H, the 

 third 10 H, the fourth 20 H, and the fifth 40 H. 

 Then the control and irradiated seeds were 

 planted in soil rich in nutritious substances. 

 Observation of the sprouts revealed that seeds 

 receiving doses of 5 and 10 H units germinated 

 simultaneously with the control seeds; those 

 receiving 20 units germinated considerably 

 later, and those receiving 40 units did not 

 sprout. Further observations of their develop- 

 ment showed that while the control plants de- 

 veloped very fully, the irradiated plants showed 

 progressively poorer development in proportion 

 to the increase of their exposure to radiation. 



The experiments of Promsy and Drevon 

 (1912) are interesting because they dealt with 

 the effect of temperature on the sensitivity of 

 plants to X rays and the rays were used in 



