ULTRA-VIOLET AND SEED PLANTS 871 



summary of any favorable results under vita glass being due to the 

 region 2900 to 3100 A alone. Favorable results mentioned for plants 

 grown under vita glass are ascribed rather to "the more extensive 

 irradiation under vita glass," and there is mentioned the desirability 

 of separating infra-red and ultra-violet effects. They recognized the 

 high transmission of vita glass in the infra-red. At the end of the paper 

 they state that "the present investigation is hardly more than a limited 

 survey" and that "for conclusive results each species tested would 

 require further examination." 



Regarding the interpretation of the differences found in plants under 

 vita glass as compared with those under common glass it is evident that 

 the authors attach great significance to slight differences in favor of 

 vita glass, which have been obtained with small plant populations not 

 grown under carefully controlled conditions and often not checked by 

 repeated experiments. 



The most consistent "compositional response" to vita glass was 

 an increased percentage of lipids in the dry matter. In five out of 16 tests 

 the ether extracts from plants under vita glass were either lower or no 

 higher in lipids than were those under ordinary glass. The other 11 cases 

 showed slightly higher percentages for plants under vita glass. In 

 another paper (Tottingham, 114) a higher percentage of lipids for 

 tomato plants under vita glass is again reported. 



While these percentages are small, the fact that increases have been 

 reported in a number of cases may indicate a vita glass effect. Certainly, 

 however, from such experiments we are not justified in attributing this to 

 effects of the region 2900 to 3100 A alone. 



Miss McCrea (56 to 59) has studied the growth of the plants and the 

 medicinal potency of the tincture obtained from Digitalis purpurea grown, 

 in the seedling stage, under vita glass and under common glass and then 

 transplanted to the open. She states that "during the 6 to 8 weeks of 

 exposure, treated plants clearly show an advantage over controls. They 

 are larger, of darker green, and develop the second, third, and fourth 

 pairs of leaves earlier than do the controls." These visible differences 

 disappeared after the plants were grown in the open. When these plants 

 were harvested, after having been grown in the open from about May 25th 

 to late July or early August (first crop) or to mid-September (second 

 crop) tinctures made from the dried, treated plants gave increased potency 

 over those of controls to the extent of 11.66 per cent to 51.50 per cent. 

 This increased potency was also found to be carried over to the second 

 year in these plants. Any possible solarization of the glass she used 

 failed to affect the results. 



While her results are very interesting, she has not measured the 

 radiation under the t\^o kinds of glass and hence we are left in doubt as 

 to how much of the effects noted can be attributed to ultra-violet. 



