PREVIOUS INVESTIGATIONS UPON PLANTS 59 



resistant to the rays, not being at all affected by an intensity of ray 

 that calls forth a strong reaction in Vicia Faba. If the rays are not 

 sufficiently strong no retardation occurs at all. Roots whose growth 

 is inhibited by the rays for a certain period will resume their growth. 

 The centgener power of seeds was not affected by two exposures to 

 rays of the intensity employed (20 Holzknecht units), and the author 

 suggests that perhaps Rontgen rays of a certain intensity may act as 

 a stimulus to germination, but such experimental effects were not 

 recorded. Further results obtained by Kornicke by treatment with 

 X rays are mentioned in connection with his experiments with 

 radium. ^^' *^ 



2. Effects of Radium Rays on Plants. 



The first recorded observations of the effects of radium rays on 

 plant tissues were made by Giesel,^^ two years after Madam Curie's 

 discovery. He announced that the rays produced a bleaching of the 

 chlorophyll in leaves, causing them to assume an autumnal yellow 

 throughout, with a brown coloring on the side exposed to the radium. 

 Paper in which radium preparations have lain for a long time becomes 

 brown and brittle, and celluloid loses its firmness. These effects of 

 intense radium rays, said Giesel, hint at a molecular rearrangement, 

 whereby their physiological effects upon plant and animal cells may 

 be explained. 



Aschkinass and Caspari^ reported that Becquerel rays "of the 

 second type" (/3 rays), as well as X rays, are injurious to bacteria, 

 and a few weeks before this Becquerel ^^ announced that an exposure of 

 a week or more to radium rays destroyed the germinating power of 

 seeds of cress and white mustard. Negative results followed an 

 exposure of only 24 hours. These experiments were made in Bec- 

 querel's laboratory by Louis Matout. 



Danysz '* studied the pathogenic action of the rays and " emana- 

 tions " * given off by radium on different tissues and organisms, and 

 found that all species of bacteria are hindered in their development 

 by radium rays, but that certain kinds, notably those which produce 

 proteolytic enzymes, are more sensitive than others, and are killed 

 under certain conditions of exposure. 



* As explained in Chapter I, there is but one " emanation " given oft" by radioac- 

 tive substances. It is difficult to know to just what Danysz refers bj "emanations." 



