152 PLANT LIFE. 



often of a dull reddish-yellow, which contrasts with the 

 green of the older leaves. There is little doubt that this 

 red colour is due to a substance called anthocyanin, 

 which is in some way protective, though there is some 

 dispute as to its exact function. Some suppose that 

 it is merely a sun screen protecting the young tissue 

 below from the injurious effect of too strong a light. 

 Others maintain that this substance changes the light 

 rays into heat, and thus assists in the chemical trans- 

 formations going on in the leaf. From the point of 

 view of an open-air botanist, the former theory is 

 very satisfactory, for this colour certainly does appear 

 exactly in the positions in which, on that supposi- 

 tion, it would be expected. The leaves of the 

 Colt's-foot, of the Hawthorn, and of the Daisy, are 

 all in their youngest state when they first become 

 exposed to the light, nearly erect, so that they 

 receive the light upon their edges, not upon the flat 

 surfaces of the leaf All along these exposed edges 

 are small glistening knobs placed at the ends of the 

 veins and coloured red. When the leaf is very young 

 these knobs are close together, and would, if the theory 

 be sound, decidedly protect the young leaf from sun- 

 scorch. They could scarcely be of much use on the 

 second theory. These little round red points can be 

 seen even on the mature leaf; but whereas the green 

 part between them has enormously expanded, they are 

 practically precisely the same size as they were when it 

 had scarcely developed at all. These small, usually 

 unnoticed dots show very nicely how a minute detail, 

 which one would suppose useless, may be of the very 

 greatest importance in the life-history of the plant. 

 The gummy or varnished character of young leaves 

 is also certainly of some protective value to them ; it 



