34 RADIOACTIVITY A FACTOR OF PLANT ENVIRONMENT 



gram of " pure" radium emits a quantity of heat equal to lOO gram 

 calories per hour, or 2,400 gram calories in one day — nearly enough 

 to dissociate one gram of water (3,900 gram calories).* 



Relative Importance of the Emanation : A large part of 

 the radioactivity to which the sub-aerial portions of plants are exposed 

 is due to the emanation diffused in the atmosphere. Rutherford 

 states that about three fourths of the activity of radium is due to the 

 emanation, and he has calculated that, if we could get i c.c. of 

 radium emanation, it would raise to a red heat the glass tube con- 

 taining it, and light up an X ray screen brilliantly through one foot 

 of solid iron. This evolution of energy would continue for several 

 days without much change, and would be appreciable after one 

 month. 



This chapter contains a portion of the evidence, accumulated 

 during the past ten years or more, that radioactivity and free electrons 

 are ecological factors, a part of the normal environment of probably 

 every plant. Undoubtedly there will be considerable modification of 

 detail as the science progresses, but the main fact of the wide distri- 

 bution of radioactivity in nature seems now to be firmly established. 

 In what way, and to what extent it influences physiological processes 

 and morphological expression remains largely to be determined. 



Bibliography 



1. Acolla, G. Boll. Accad. Gioenia Sci. Nat. Catania, p. 22. 1907. 



(Not seen.) 



2. Adams, E. P. Water rodioactivity. Phil. Mag. VI. 6 : 563. 1903. 



3. Allan, S. J. Excited radioactivity produced from atmospheric air. 



Proc. & Trans. Roy. Soc. Canada, II. Trans. 1902^: 71. 1902. 



4. . Radioactivity from freshly fallen snow. Phys. Rev. 16: 237. 



1903. 



5' • Radioactivity of freshly fallen snow. Phys. Rev. 16: 306. 



1903. 



6. . Radioactivity of the atmosphere. Phil. Mag. VI. 7 : 140. 1904. 



7. Allen, H. S., & Blythswood, Lord. Radio-active gas from Bath mineral 



waters. Nature 68 : 343. 1903. 

 S. Ayrton, H. Note on electric charging and discharging at a distance. 

 Nature 65 : 390. 1902. 



* Though Paschen ^'^ finds reasons for thinking that 50 per cent, of the heating 

 effect is due to the gamma rajs, the experiments of Rutherford and Barnes ^^" indicate 

 that this effect is due mainly to the bombardment bj the a rays. 



