764 BIOLOGICAL EFFECTS OF RADIATION 



Pleasanton's results with grapes led him to experiment further with 

 hogs and with a bull calf, with both of which equally phenomenal results 

 were obtained. In his final statement he says : 



"These, gentlemen, are the experiments about which your curiosity 

 has been excited. If by the combination of sunlight and blue light from 

 the sky, you can mature quadrupeds in 12 months with no greater supply 

 of food than would be used for an immature animal in the same period, 

 you can scarcely conceive of the immeasurable value of this discovery to 

 an agricultural people ! ... In regard to the human family, its influence 

 [i.e., blue light] would be widespread . . . you could not only in the 

 temperate regions produce the early maturity of the tropics, but you 

 could invigorate the constitutions of invalids and develop in the young, 

 a generation, physically and intellectually, which might become a marvel 

 to mankind. Architects would be required to so arrange the introduction 

 of these mixed rays of light into our houses that the occupants might 

 derive the greatest benefit from their influence. Mankind will then not 

 only be able to live fast, but they can live well and also live long." 



If "ultra-violet radiation" were substituted for "blue light" in this 

 statement, it would sound not unlike many of the more recent accounts 

 of "the powerful ultra-violet ray." 



While Pleasanton's paper is undoubtedly an extreme case, it does 

 illustrate the inaccuracy of the work of this period. It is not surprising 

 that there was little agreement among different investigators as to results 

 obtained with glass of different colors. It was not until comparatively 

 recently that improved methods of making glass and better instruments 

 for measuring and controlling radiation made it possible to conduct more 

 exact and more reliable experiments. 



Except for a few outstanding cases, the present review will be 

 restricted to the more recent work on the effect of different regions of the 

 visible spectrum on seed plants. Since the relation of light to photo- 

 synthesis, chlorophyll development, seed germination, enzymes, and 

 general metabolism, and the effect of radiation on lower organisms are 

 being considered elsewhere in this monograph, they will in general be 

 omitted here. This discussion will center around growth and develop- 

 ment, composition, fresh and dry weight, miscellaneous physiological 

 effects, and reflection, absorption, and transmission of radiation by leaves. 



GROWTH AND DEVELOPMENT 

 GENERAL STUDIES 



Pfeffer (30) summarizes the status of the question of the effect of 

 rays of different wave-lengths up to his time when he says : 



"Although the less refrangible rays are most active in photosynthesis, 

 it is the more refrangible ones (blue to ultra-violet) which exercise the 

 greatest influence upon growth and upon irritable movements or curva- 



