EFFECT OF X-RAYS ON RATE OF CELL DIVISION. 89 



Certain others of Gager's observations on the effect of radium 

 on plants are concerned with the problem of growth. He reports 

 among his results a cessation of cell division, an acceleration of 

 differentiation, a decrease in cell size, and a lack of coordination 

 in histogenesis. Those processes which go to produce senescence 

 are accelerated. 



Guillemont compared the action of X-rays and of the beta rays 

 of radium upon plant cells. He obtained a standard for com- 

 parison and found that, the flourescent effect of the two being 

 equal, the beta rays were more intense. The characteristic 

 action is a retardation of the growth, when the rays are fairly 

 strong. He determined also the fatal strength and a compara- 

 tively weak strength at which the rays perhaps accelerate. 



Becquerel likewise found that weak, or short, stimuli had small 

 effect, while longer ones retarded ^growth. Exposing seeds for a 

 day had little effect upon their power to germinate, but exposure 

 for a week or more inhibited germination. Pollen germination 

 is also inhibited, according to Lapriore, by exposure to X-rays. 



Maldiney and Thouvenin, however, early reported that germ- 

 ination of seeds was hastened by exposure to X-rays. 



Gager obtained retardation of growth following exposure of 

 seeds under various conditions. The amount of retardation 

 varied directly with the strength of the radiation. Some kinds 

 of seeds, exposed to radium of weak activity, later showed ap- 

 parent recovery. It has been shown that hydrogen and hydroxyl 

 ions stimulate germination. Gager says with regard to this, 

 'If the radium rays produce ionization in the mineral solutions 

 in the soil then these ions would act as a stimulus to plants 

 growing there, and, under suitable conditions, cause an accelera- 

 tion of growth. It is not improbable that the results recorded 

 above are due to a combination of both causes, that is, to the 

 direct action of the gamma rays combined^with that of ions pro- 

 duced by the rays in the soil-solution." 



Gager in his memoir discussed at length the workjdone previous 

 to 1908 upon both plants and animals. The results upon which 

 there is any very general agreement, he summarizes in the fol- 

 lowing eight statements: 



"i. Radium rays have the power to modify_the life-processes 

 of both plants and animals. 



