154 MEMOIRS OF THE NEW YORK BOTANICAL GARDEN 



act as a stimulus to plants; up to an optimum point the response 

 is an acceleration of function, but beyond the optimum the 

 response is a depression of function, culminating under certain 

 conditions in complete arrest of physiological activity, or in the 

 death of the tissue or organism. 



Among those who have contributed to the literature of this 

 subject since 1908, may be mentioned Crochetelle (1913), Doumer 

 (1912), Fabre (1910-11), Molisch (1912-13), Petit (1913), Petit 

 & Ancelin (1913), Stoklasa (191 2-14), and Vacher (191 3). It is 

 significent to note that in characteristic European fashion, prac- 

 tically all of the papers published on the continent contain no 

 reference to the Memoir of the New York Botanical Garden, 

 though in a few rare instances a short "popular" paper by the 

 author of that Memoir is cited. 



Results of chemical study of very considerable significance in 

 connection with the subject of photosynthesis, were presented by 

 Stoklasa, Sebor, and Zdobnicky, in 1911 and 1913. These experi- 

 ments^ deal with the synthesis of sugars from CO2 and nascent 

 hydrogen, in the presence of K2CO3, under the influence of radium 

 rays. Formaldehyde polymerized in the presence of potassium 

 carbonate is stated to result in the formation of reducing sugars. 

 A hexose and pentoses were positively noted, but no ketoses. 

 This work has not been confirmed by other investigators. Since 

 radioactivity is a constant and universal factor of plant environ- 

 ment the hypothesis that it may be concerned in the baffling 

 process of photosynthesis is, to say the least, very attractive, 

 and worthy of painstaking investigation. But the writer is 

 inclined to believe that radioactivity is not involved as a normal 

 factor in photosynthesis, even though it may, under certain con- 

 ditions, favor the artificial synthesis of carbohydrates. 



In connection with experiments, now in progress, on the use 

 of radium-rays in medicine, and especially in the treatment of 

 cancer and tumors, it is of the utmost importance to keep in mind 

 that under certain conditions of exposure the malignant growth 

 may be accelerated rather than retarded; but experiments with 

 plants as well as with animals show that embryonic tissue is much 

 more sensitive than mature tissue to radium-rays, and therefore 



' Biochem. Zcitsch. 30: 433-456. 1911. Compt. Rt-nd. Acad. Sci. Paris 156: 

 646-648. 19 1 3. 



