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called N rays by plants of the garden cress was reported by 

 Meyer/ Their emission, he said, varies with the activity of the 

 protoplasm, and is diminished when the plants are exposed to the 

 vapor of chloroform, and is modified by mere compression of the 

 tissues. 



In 1904 Russel '^ described before the Royal Society the rather 

 startling discovery of the action of wood on a photographic plate 

 in the dark. This property, he said, belongs probably to all 

 woods. Conifers are especially active, and the spring wood most 

 of all, but the dark autumn wood produced no such effect. Oak, 

 beech, acacia {Robinia), 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. Ex- 

 posure to sunlight, especially to the blue rays of the spectrum, 

 increases the activity. Cork, printer's ink, leather, pure India 

 rubber, fur, feathers, and turpentine 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^' ^ papers were also published in 1904. He re- 

 ported that all freshly gathered plants, fruits, flowers, and leaves 

 possess a radioactivity which is stronger in the young and in in- 

 dividuals in action than in those at rest, being apparently propor- 

 tional to the vital energy. For this phenomenon he proposed 

 the term bio-radioactivity . Buds of lilac, and leaves of TJmja 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 ema- 

 nation, the seedlings growing from such seeds showed induced ra- 

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

 inactive. Also when a mature plant was exposed to the emana- 

 tion the roots became strongly radioactive, the stem somewhat 

 less so, the leaves only slightly, and the flowers not at all. 



