104 ANNUAL IIEPOIIT SMITHSONIAN INSTITUTION, 1937 



metliod. The new apparatus has been duplicated in our shop for in- 

 tensive use in photosynthetic studies. We expect to observe photosyn- 

 thesis quantitatively in various families of plants. 



Dr. McAlister published preliminary results of a research on time 

 relations in photosynthesis. He showed that intermittent illumina- 

 tion gives very dilferent growth rates depending on the rapidity of 

 intermittance. With alternations of light and darkness 60 times f)er 

 second the growth rate over a period of several hours was actually 

 twice as rapid as with continuous illumination of an equal total quan- 

 tity of light supplied. Owing to the practically instantaneous char- 

 acter of his measurements, he was able, for the first time, in studies 



3500 4500 5500 6500 7500 



WAVE UENGTH 

 FiGDUE 1. — Wave-lengUi assiuiilaUon curves. 



of plant physiology, to turn on the light and continuously follow what 

 happens in plant growth. INIany most interesting observations were 

 recorded.^ 



In a cooperative research with Dr. Flint, of the United States Dc- 

 j)artment of Agriculture, Flint and McAlister examined the efficiency 

 of different wave lengths of light to promote germination in light- 

 sensitive lettuce seed.^ Their results tie in most suggestively with the 



^ Smlthsouian Misc. Coll., vol. 95, no. 24, pp. 1-17, figs. 1-10. pis. 1. 2. 1937. 

 » Smithsouian Misc. Coll., vol. 9G, no. 2, pp. 1-8, figs. 1, 2, pi. 1, 1937. 



