436 EFFECT OF LIGHT [Ch. XVU 



these are of an injurious character ; in the second, they favor 

 the metabolic growth processes. Long-waved light, on the 

 other hand, has usually no more effect than darkness, or the 

 absence of light. However, upon germinating ferns and 

 grasses long- waved light has' a decided accelerating effect. 

 Since even in daylight growth occurs faster than in the dark 

 we must conclude that upon these organisms the blue rays do 

 not seem to exert an injurious effect ; they are, as it were, 

 blind to the blue rays, and hence experience no freedom from 

 restraint in the dark, and, unlike seedlings, no excessive growth 

 there. 



4. The Cause of the Effect of Light on the Rate of Growth. 

 — The action of red rays upon growing phanerogams requires 

 no special explanation here. It is clear, from what we already 

 know, that an etiolated seedling, or alga, can develop only in 

 the presence of the red rays, which are ordinarily essential to 

 its nutrition. Consequently, we find that red rays do not 

 hinder the growth of ordinary seedlings, but cause etiolated 

 green plants as well as seedlings of ferns and grasses to grow 

 faster than they would in the dark. 



The action of the blue ray does, on the other hand, demand 

 more detailed consideration, for it seems at first as if its 

 diverse effects upon plants and animals constitute a great diffi- 

 culty. Why should the same rays retard the growth of aerial 

 organisms and accelerate that of water animals ? In inventing 

 an hypothesis to fit the case, we have first to recognize that the 

 action of the blue ray is a chemical one, and is probably of the 

 same kind upon all organisms. It must, consequently, be that 

 the degree of the effect is different. This difference may be 

 due either to a difference in the quality of the different proto- 

 plasms or to a dissimilarity of the external conditions under 

 which the effect is produced. We may say that, either on 

 account of the presence of abundant free oxygen in the air, or, 

 perhaps, on account of a greater lability of plant protoplasm, 

 the blue rays effect such extensive transformations (oxidations, 

 Quincke, '94) in aerial plants as to interfere with growth, 

 possibly, by promoting loss of water. Upon water organisms, 

 on the other hand, only slight metabolic changes occur, which, 

 on the whole, favor the imbibitory or assimilative processes. 



