The Prevalence of Green Color in Plants 39 



its most striking, though a temporary, development in the young 

 shoots of a good many plants (e. g., Maples, Oaks, and many 

 herbs), which it flushes with translucent rose red as they push 

 from the buds in the spring, though later it fades away with the 

 increasing rapidity and vigor of growth. In all of these cases 

 the color resides in a particular substance, named erythrophyll 

 (or anthocyan), dissolved in the sap of the cells, from which.it 

 can usually be extracted by hot water. It is typically a beautiful 

 deep rose red material, varying much, however, in tint according 

 to the conditions surrounding its formation, and the substances 

 with which it is associated. Its identity, therefore, is plain enough, 

 but concerning its significance to the plant there is very much 

 doubt. One explanation argues thus; erythrophyll, as its color 

 implies, permits the red rays of sunlight to pass unaltered,' but 

 cuts off, or at least weakens, the blue-violet ones. Now it is 

 known that the red rays, while the most useful in photosynthesis, 

 are harmless to the living protoplasm, but the blue-violet rays, 

 though also useful in photosynthesis, are injurious, when un-^ 

 tempered, to the living protoplasm and detrimental to some of 

 the physiological processes; therefore (runs the argument), the 

 erythrophyll probably acts as a protective screen, especially in 

 the case of the early spring vegetation, admitting the beneficial 

 red rays and tempering the noxious blue-violet rays until the 

 formation of the chlorophyll, which, while developed for a differ- 

 ent purpose, incidentally acts as a protection to the protoplasm, 

 a subject to which, by the way, we shall return for fuller discussion 

 in the later chapter on Protection. A second explanation is based 

 upon the fact that erythrophyll has been found to possess a not- 

 able power of transforming light into heat; it must therefore 

 serve, this argument holds, to warm the tissues which possess 

 it, and thus, during the bright but cool days of the spring, must 

 facilitate those processes, such as nutrition, translocation of food, 

 and growth, which are promoted by warmth. More recently a 

 third explanation has been offered, based upon the fact that when- 



