THE FUNCTIONS OF RADIATION IN THE PHYSIOLOGY 



OF PLANTS 



I. GENERAL METHODS AND APPARATUS 



By F. S. BRACKETT and EARL S. JOHNSTON 

 Dh'ision of Radiation and Oriianisnis, Smithsonian Institution 



[With One Plate] 



Radiation undoubtedly affects many of the physiological processes 

 of plants in addition to the well-recognized ones of photosynthesis and 

 phototropism. To what extent these and other reactions may influence 

 each other, if at all, is wholly an open question. Since it has been im- 

 possible to produce artificially any process which bears a close similar- 

 ity to those found in the plant, one must perforce seek as complete 

 data as can be obtained from direct studies of plant behavior. Modi- 

 fications of the two essential light characteristics, wave length and 

 intensity, may in general affect not only the reaction which is being 

 given particular attention, but also other photochemical reactions 

 which take place in the plant. So far as observational data are con- 

 cerned one is limited to numbers which represent overall effects, that 

 is, gas interchange, change in dry weight, change in height, change in 

 shape, change in color, etc. Anyone who assumes that one of these 

 overall numbers may be varied without influencing another must cer- 

 tainly accept the burden of the proof. 



Consequently it is our view that investigations of photosynthesis can- 

 not safely be interpreted without due consideration of problems of 

 growth and characteristic plant behavior. It has therefore been our 

 purpose to supplement our investigations of photosynthesis with ex- 

 periments to determine the ways in which changes in intensity and 

 wave length affect the characteristics of plant behavior. In order that 

 such investigations of the light variables may yield data which are 

 reproducible and significant, it is of course necessary that other varia- 

 bles be maintained constant and as far as possible defined as to magni- 

 tude. Obvious as such a consideration is, failure sufficiently to realize 

 this demand has contributed to a considerable degree to the chaotic 

 results found scattered through the literature. However, to create 

 conditions under which the physical and chemical factors of environ- 

 ment can be sufficiently well controlled and defined is by no means a 

 simple problem. 



Smithsonian Miscellaneous Collections, Vol. 87, No. 13 



