SMITHSONIAN MISCELLANEOUS COLLECTIONS 



VOL. 95 



Other light in a suitable box. For lateral radiation a plane mirror was 

 employed at an angle of 45° to reflect a horizontal beam onto the plant 

 parts maintained always in an erect position during the experiments. 



EXPERIMENTATION 



INFLUENCE OF GENERAL RADIATION UPON GROWTH SUBSTANCE 

 IN COLEOPTILE TIPS 



Avcna sativa. — Intact coleoptiles growing in water cultures were 

 subjected to radiation vertically incident upon the tips for different 

 lengths of time, while control plants of the same size were kept in 



Table i. — Influence of Mercury Arc Radiation on Growth Substance 

 Intact tips illuminated vertically {Avena) 



» 9 tests made, 

 b 8 tests made. 



Note. — In all tables total arc refers to that portion of the mercury arc radiation transmitted by 

 glass and 5 cm water. 



darkness. Immediately following the period of irradiation, apical 

 3-mm portions were excised from the plants, and these were placed 

 unilaterally (with a little 5 percent gelatin) upon decapitated Avena 

 test plants. Darkened control tips were tested in a similar manner. 



The blue mercury line, 4358 A, was used to illuminate different sets 

 of intact plants for 55, 180, and 300 minutes. Resulting curvatures 

 of the test plants showed only small and perhaps insignificant differ- 

 ences in growth substance in these irradiated tips as compared 

 with the darkened controls (table i). 



Intense light from the total arc filtered through glass and 5 cm of 

 water was used in the same manner as stated for the blue light. In 

 this light, growth substance content of the tips was reduced appre- 

 ciably by exposure for 120 minutes (table i). Averages for four 



