872 BIOLOGICAL EFFECTS OF RADIATION 



Recently Leonard and Arthur (48) have reported on experiments 

 which have been in progress for three years in which no significant differ- 

 ences in glucoside yield could be observed between digitalis plants grown 

 under a glass having a higher ultra-violet transmission and those grown 

 under ordinary window glass, whether the plants were kept until sampled 

 in air-conditioned greenhouses or were set out after some months of such 

 treatment into the open field. 



In England there have been numerous reports on plants grown under 

 the English vita glass including those of Russell (83), the Kew Gardens 



(42), Saleeby (86), H (35), Colman (12), Westfield College (121), 



Haddock (49), Thomson (111), Graham and Stewart (33), Tincker (112, 

 113), Pilkington (66), and Secrett (92). In Germany results of experi- 

 ments on plants grown under the various German glasses of this type have 

 been made by Kache and others (41), Dix (24), Herold (36), Reinhold 

 alone and with others (77 to 79), Roeder (80), Grossman (34), and an 

 anonymous author (1). A detailed review of these experiments is not 

 necessary here inasmuch as the majority of them were ordinary green- 

 house experiments without adequate controls and all of a very prelimi- 

 nary nature. As might be expected, there is no general agreement 

 among them as to the results obtained. 



In Sweden Lamprecht (47) has carried out one of the most careful 

 investigations of this type. He has compared plants grown under Helasan 

 glass which transmits about 50 per cent of the solar radiation from 2900 



o 



to 3100 A, a somewhat higher percentage of ultra-violet than vita glass 

 transmits, but not so high a percentage as Uviol glass transmits. The 

 plants were carefully handled and spaced and environmental conditions 

 made as uniform as possible. Great care was taken to have the thickness 

 of glass panes comparable in the test and control houses in order that the 

 intensity of radiation reaching the plants should not vary because of this 

 factor. Relatively large numbers of plants, never less than 40, under 

 each condition in each test were used, and each series of experiments was 

 repeated several times. The results were treated statistically and 

 probable errors taken into account. Fresh-weight and dry-weight per- 

 centages were determined and various chemical analyses made. 



Six series of carrots were run with 46 to 122 experimental plants used 

 in each series. In no case did the use of Helasan glass result in signifi- 

 cantly increased fresh weight, dry weight, or any change in chemical 

 composition. One series of parsnips and one of radishes, both root crops, 

 as were the carrots, gave similar results. Two series of lettuce plants 

 gave no significant differences in fresh or dry weights related to the 

 type of glass used, but indicated a definite trend in dry weights in favor 

 of Helasan glass. Two series of spinach, again a leaf crop, gave results 

 similar to thoise of lettuce. 



The conclusion regarding the effect of the ultra-violet portion of the 

 solar spectrum as revealed by these experiments was that there was the 



