864 BIOLOGICAL EFFECTS OF RADIATION 



might justly be suspicious that intensity differences in radiation and 

 possibly a greater percentage reduction in the whole blue-violet end of 

 the spectrum under Euphos glass were in operation. Unfortunately, 

 there are no figures given of the actual intensities reaching the experi- 

 mental plants in that portion of the work in which the attempt was made 

 to equalize intensities. It might be noted that Senn (93) has attributed 

 dwarfing in alpine regions to greater light intensity there, but he gave 

 quality no consideration. 



The experiments seem to indicate that at low altitudes the elimination 

 of solar ultra-violet alone has relatively slight if any influence on the 

 plant. At higher altitudes, where solar ultra-violet is more intense, or 

 under artificial radiation rich in that portion of ultra-violet present in 

 sunlight, there are indications of possible formative effects of ultra-violet, 

 although these have not been clearly separated from intensity effects in 

 the visible, particularly in the blue-violet region. Shaw (94), and later 

 Popp (71), have emphasized the significance of the blue end in relation 

 to configuration of the plant. 



Simon (106) in a recent semipopular account of the nutrition of 

 cultivated plants mentions incidentally an experiment of his with Euphos 

 glass of the type used by Schanz. Cultures of garden plants under 

 this glass were said to give, under otherwise similar conditions of environ- 

 ment and nutritional conditions, increased yields up to 50 per cent over 

 plants grown under ordinary glass. The author, however, gives the 

 impression that he was of the opinion that Euphos glass transmits ultra- 

 violet better than ordinary glass does. If it was, as stated by the 

 author, the same glass as was used by Schanz, it eliminated the ultra- 

 violet. An accurate statement of the conditions of the experiment is 

 not given. 



INVESTIGATIONS DEALING WITH PLANTS GROWN IN DAYLIGHT WITH 

 ADDITIONAL SHORT DAILY IRRADIATION FROM A MERCURY-VAPOR LAMP 



An examination of Tsuji's (117) short preliminary paper in the 

 Louisiana Planter would convince any critical observer of the inconclu- 

 siveness of his extravagant claims. The paper is mentioned here merely 

 because it has been referred to in later reports. 



Delf, Ritson, and Westbrook (20, 21) attempted one of the first 

 studies of the effects of short daily exposures of more mature plants to 

 the radiation of an unscreened mercury arc. Young plants of Arachis, 

 Voandezia, and Trifolium exposed at various distances for short periods 

 up to 10 min. per day were stunted, the epidermis of the leaves collapsed, 

 and leaf mesophyll was less differentiated and more compact than in 

 the controls. All of the irradiated plants died after the conclusion of the 

 experiment. Of 10 controls left, 5 were irradiated for one month for 

 30 sec. per day at a distance of 8 ft. Two months later the irradiated 



