EFFECTS OF RADIUM RAYS ON PLANTS 999 



contrary to the results of Kimura in 1929, changes in the rate of carbon 

 dioxide production and cell-division do not always go hand in hand. 

 One process may be increased by exposures which retard the other. In 

 other words, the rays have a specific action on certain physiological proc- 

 esses in contrast to others. One should not, therefore, make any broad 

 generalization concerning their action on metabolism as a whole. 



In 1925, a stimulating paper was published by Blaauw and Heyningen 

 (7) on the radium-growth-response of one cell. The authors had previ- 

 ously determined experimentally that unicellular organs, such as the 

 sporangiophores of Phycomyces, and also various multicellular organs of 

 higher plants respond to light stimulus with characteristic accelerations 

 and retardations of growth. The present paper gives the results of an 

 investigation to determine whether the growth of unicellular sporangio- 

 phores, so sensitive to visible light, is also affected by radium rays. 

 The light-growth-response (visible spectrum and ultra-violet) is charac- 

 terized in these cells by an acceleration of growth (positive response), 

 beginning after at least 3 min., and changing into a temporary retardation. 

 The radium-growth-response was found to be just contrary to the light- 

 growth-response, beginning with a strong decrease of growth, then, on 

 account of a contrareaction, passing into an acceleration of growth. 

 With continued exposure the growth "recovers its equability." 



The radium-growth-response is considered by the authors as a second- 

 ary phenomenon — a result of more primary responses or modifications, 

 brought about in the metabolism of the cell by the influence of the rays, 

 "but which are for the present absolutely beyond our understanding." 

 It is of interest to compare these results and the discussion with those of 

 Redfield and Bright, above noted. 



Blaauw and Heyningen found that the radium-growth-response 

 follows more quickly than the light-growth-response; the former is per- 

 ceptible after an average of 2 min., and the latter after 3.5 min. The 

 sporangiophores of Phycomyces never showed any trace of a radio- 

 tropic curvature; the strong growth response followed a one-sided expo- 

 sure to the radium. This is explained by the fact that the radium rays 

 pass through the thin cells so perfectly that there is no difference of their 

 intensity within the cell. The experiments indicate that the radium- 

 growth-response is caused by the gamma rays exclusively. 



But just as Sierp, with Avena sativa, and later Tollenaar had demon- 

 strated dark-growth-responses for various organs, as soon as a long 

 exposure to light is stopped, so it was found by Blaauw and Heyningen 

 that, after the growth has become steady again after long exposure to 

 radium, the radium preparation cannot be removed without causing a 

 new reaction contrary to the first. This response, caused by the removal 

 of the radium rays, is called deradiation response. In other words, if 

 we define stimulus as any change in any factor of the environment, and 



