BIO-RADIOACTIVITY, EOBES, RADIOBES 75 



{Robmid), Spanish chestnut, and sycamore possess this property, but 

 ash, elm, the horse-chestnut, and the plane tree only to a slight 

 degree. Most resins manifest it, but not so the true gums, such as 

 gum Senegal and gum tragacanth. Exposure to sunlight, especially 

 to the blue rays of the spectrum, increases the activity. Cork, 

 printer's ink, leather, pure India rubber, fur, feathers, and turpen- 

 tine are reported to have their activity increased in the same way. 

 Since bodies such as slate, porcelain, flour and sugar, in which there 

 is no resinous or allied body, do not react in this way, nor affect the 

 plate at all, the activity of the various kinds of wood is attributed to 

 the resinous substances in them. Tommasina's* paper was also pub- 

 lished in 1904. He reported that all freshl}^ gathered plants, fruits, 

 flowers, and leaves possess a radioactivity which is stronger in the 

 young and in individuals in action than in those at rest, being appar- 

 ently proportional to the vital energy. For this phenomenon he pro- 

 posed the term hto-radioactivity . Buds of lilac, and leaves of Thuja 

 and of laurel were found by him to be bio-radioactive. 



In the following year Tarchanoff and Moldenhauer '^ published 

 their preliminary note on the induced and natural radioactivity of 

 plants, and on its probable role in their growth. When seeds of 

 various grains, and of the pea were exposed to the radium emana- 

 tion, the seedlings, growing from such seeds showed induced radio- 

 activity in their roots, but the stem and small leaves remained inactive. 

 Also when a mature plant was exposed to the emanation the roots 

 became strongly radioactive, the stem somewhat less so, the leaves 

 only slightly, and the flowers not at all.* 



This distribution of the radioactivity in the plant body is constant, 

 and the authors consider that there is in the plant a special substance, 

 sensible to the emanation, and capable of becoming radioactive under 

 its influence. This substance occurs in the roots, but gradually 

 diminishes up the stem. It is found also in seeds. According to 

 this same paper plants possess a natural radioactivity, which is dis- 

 tributed throughout the plant similarly to the induced radioactivity. 

 This natural radioctivity is strong enough to affect a photographic 

 plate, and plays an important role in the development of the plant. 



In a second paper Russel*^ gives a list of 33 native and 22 foreign 

 woods that are active, and says that the activity of resins and gums 

 is increased by exposure, not only to sunlight, but to the arc-light as 



* Results not confirmed by Acqua, Rend. Accad. Lincei V. 6 : 357. 1907. 



