§ 1] UPON THE RATE OF GROWTH 435 



These series run then in order of effect on growth exactly par- 

 allel to the series obtained from the growing tadpole, and are 

 very similar to the series obtained by Beclard for the blow- 

 fly. 



There are certain a priori grounds for believing that 

 Beclard's series is the more correct, not only for growing 

 flies, but for all animals. We would then get for a curve of 

 relative effect of the different parts of the spectrum upon 

 growth something like Fig. 126, I.* The conclusion to which 

 all these experiments point is this : the accelerating effect of 

 weak white light upon the growth of animals, contrary to the 

 case in plants, is due to the short-waved rays. 



The alleged peculiar effects of the green rays cannot go 

 nnnoticed. These seem to have been first insisted upon by 

 Bert ('72, '78), who found that in the green lantern the 

 young sensitive plant lost sensibility and died in three or four 

 ■days, which is about the time in which they would have died 

 in complete darkness. This observation has been confirmed 

 by several experimenters ; for example, by Keatjs ('76, p. 8), 

 Adeianowsky ('83), Villon ('94, p. 461), and Gautibr 

 ('95) for plants, and by Schnetzler and by Yung for tad- 

 poles. Yet, on the other hand, Flamsiarion" ('95) found no 

 peculiar action of green light upon the sensitive plant. In 

 the absence of precision in the opposing statements, we may 

 doubt whether green rays, as such, produce any positive harm. 

 It is probable that they are neutral in growth. 



Summing up the results of our study on the effective rays in 

 the modification of growth by light, we find that retardation, 

 as it occurs in most aerial plants, is due to the chemically 

 active rays ; that acceleration, as it occurs in animals, is like- 

 wise due to the same rays. Both effects must be due to chem- 

 ical, metabolic changes, induced by light : in the first class, 



* The favorable effect of violet or blue rays was noticed also by Villon ('94, 

 p. 463) upon sillivrorms. Here may be mentioned the "blue glass" rage of 

 twenty years ago, which was largely due to the writings of General A. J. 

 Pleasonton ('76), which, while containing a basis of truth experimentally 

 obtained by the author, were of a highly uncritical and even sensational char- 

 acter. 



