PREVIOUS INVESTIGATIONS UPON PLANTS 57 



with the typhus bacillus, Wittlin ""'^ with Bacillus coli-comtmmis, B. 

 typhi, diphtheria bacilli, Staphylococcus aureus, Spirochaeta cholerae, 

 and Tyrothryx tenuis Duclaux ; Beck and Schultz" with various 

 bacilli ; Atkinson ^ with bacteria ; and Freund,^ who exposed bac- 

 teria to both X rays and the rays from uranium. 



Rontgen rays were found either to inhibit growth or to kill by 

 Rieder^-'^^ with B. prodigiosus, the cholera bacillus, and other forms ; 

 by Tolomei'^^ with B. anthracis; by Strebel'^" with bacteria exposed 

 to Becquerel rays; and by Aschkinass and Caspari^with bacteria 

 exposed to Becquerel rays and to cathode and X rays. Rieder's 

 results disagree with those of Kriiger and Friedenthal, who, he says, 

 state that bacteria could be killed only when electricit}^ is conducted 

 through the culture, thus by electrolysis, forming anti-bacterial sub- 

 stances. He states that he carefully excluded from his cultures any 

 possible influence from heat rays, rays from fluorescent light, and 

 electric currents. 



In 1897 Atkinson * reported that etiolated plants recovered their 

 green color less rapidly than normally after exposure to the rays, 

 and interpreted this as suggesting some injury to the chloroplasts. 

 No other influence was observed, and studies on the absorption of 

 the rays by species of Mucor, bacteria, and Oscillatoria gave nega- 

 tive results. On the question of the absorption of the rays by the parts 

 of plants, however, Hinterberger ^^ had already shown that fruits 

 containing little sap, and large cavities, such as beans and pea pods 

 are most easily penetrated by the rays, while thick buds and fleshy 

 fruits, such as pears and cucumbers, are very impenetrable. 



Lopriore " studied the action of X rays on the protoplasm of the 

 living vegetable cell. With an exposure of not more than half an 

 hour the protoplasmic streaming of Vallisneria spif-alis was accel- 

 erated. After this time, if the influence of the rays is removed, the 

 motion again becomes normal. An exposure for one hour is dele- 

 terious ; the protoplasm continues to stream, but takes on a yellow 

 tint, and becomes vacuolated and granular. After an exposure of 

 two hours the streaming had not ceased, but the chloroplastids had 

 begun to fade. Pollen-grains of Genista and of Darlingtonia did not 

 germinate while exposed to the rays, but began to do so after the 

 influence of the latter was removed. 



In 1898 Atkinson^ reported negative results from experiments 

 with germinating seeds, seedlings, and mature seed plants, Mucor^ 



