X-RA Y EFFECTS ON GREEN PLANTS 963 



Evidence from experimental work reviewed in this paper indicates 

 that a majority of those who have made repeated experiments using 

 large numbers of seeds have found that light doses do not cause increased 

 germination or increased growth in vegetative parts. 



EFFECT UPON SEED GERMINATION AND EARLY GROWTH 



Historical Account of Work up to 1924. — Three years after Rontgen 

 discovered the X-rays, Maldiney and Thouvenin (40) published a state- 

 ment to the effect that X-rays hastened the germination of seeds of 

 Convolvulus and Lepidium. Ancel (2), who criticized these studies 

 because of the small number of seeds used, employed hundreds of seeds 

 of the same species and found that in no case was germination of the 

 seeds hastened by irradiation, 



Koernicke (26), in 1904, using two species of Vicia and Brassica, 

 referred to growth checking followed by a growth acceleration which 

 was transitory if the dose were not too strong. In a later research (27), 

 using many species of plants to test the practical use of roentgen irradia- 

 tion in agriculture, he concluded that X-rays parallel other rays 

 in showing growth retardation with stronger doses but growth stimulation 

 with weaker ones. He also found that with air-dried seeds germination 

 of those strongly irradiated occurred sooner than with those weakly 

 irradiated and sooner than the controls. Ancel (2), who repeated 

 the experiment with Brassica napus, using 16 lots of 100 seeds each, 

 found that radiation applied on the dry seeds in doses varying from 

 0.5 to 20 H did not hasten germination. 



Miege and Coupe (41) reported stimulation of growth in Raphanus 

 and Lepidium which manifested itself in increased weight of leaves of 

 irradiated plants as well as by increase in total weight. Daily doses 

 of 2.5 H were found to cause greatest acceleration. These positive 

 statements of results are open to criticism because they were based on 

 groups of 10 seeds in each experiment. Later investigators have shown 

 that only by using large numbers of seeds and by repeating the experi- 

 ments several times can one avoid misinterpreting results. 



Pfeiffer and Simmermacher (49) claimed that the germination of 

 Vicia Faba was increased by short exposures to X-rays but lessened by 

 long exposures. E. Schwarz (57) also found accelerated growth in 

 V. Faba with the use of weak irradiation. His work has been criticized 

 by Komuro (30) for the smaller number of experiments and for the 

 lack of controlled conditions under which the experiments were con- 

 ducted. Jiingling (23), using the same species, found that the effect of 

 raying the seeds or seedlings can be either stimulating or depressing. He 

 used an erythema dose, designated by Seitz and Wintz as the "Hautein- 

 heitsdosis" (H.E.D.). WTien a light dose of 5 to 6 H.E.D. was given, root 

 growth was unaffected while shoot growth was increased. Halberstaedter 



