430 EFFECT OF LIGHT [Ch. XVII 



red light, as in darknegs, the greatest growth occurred ; under 

 the blue light no growth had occurred, i.e. less than under 

 the clear glass. The order of height was thus : blue, white, 

 green, red ; that of the vigor of vegetation was : blue, green, 

 white, red. The peculiarly injurious effect of the violet and 

 ultra-violet rays is shoAvn also in the deleterious action of 

 electric light, which is rich in these rays (Siemens, '80, '80% 

 '82). All the foregoing observations are thus in accord, and 

 indicate that the retarding action of white light upon seedlings 

 is the resultant of the accelerating and the inhibiting actions 

 of the different rays. 



Among fungi we have observations by Vines ('78) which 

 show that Phycomyces nitens, subjected intermittently to the 

 action of darkness on the one hand, and of white light, blue 

 light, or yellow light, on the other, suffered a similar retarda- 

 tion in white and blue light, while in yellow light no marked 

 retardation occurred.* Bacillus ramosus (Fig. 123) grows 

 behind a red screen as in darkness ; behind a blue screen (of 

 CuSO^) its growth is retarded as in daylight (Ward, '95, 

 p. 381). 



Among algse FAJONTZiisr ('67) has found that Spirogyra 

 which has been kept in the dark until all of the starch is con- 

 sumed grows more rapidly in the successive members of this 

 series: darkness (no growth), blue light, full lamplight, yellow 

 light. Here we see that, while a certain amount of light is 

 necessary to the metabolism of the etiolated alga, growth, as a 

 whole, is favored by the absence of blue rays. 



Animals which are symbiotic with algse flourish or decline 

 with the latter. Accordingly, Yung ('92) has found that 

 Hydra viridis,t which has this kind of symbiosis, grows more 

 rapidly in the successive members of the series : darkness 

 (fatal), violet, green, white, and red. This series is essen- 

 tially that just given for algse living alone. 



* Kkaus ('76) says that Clavioeps growing in daylight attains a length of 

 only 4 to 6 mm. ; in green rays, 17 mm. ; in yellow and blue, each, 30 mm. ; 

 and, in the dark, 36 mm. Not much weight can be given to this statement, 

 since an account of methods is lacking. 



t A similar result was obtained with the green turbellarian Convoluta 

 Schultzii. 



