COL OB IN FLOWERING PLANTS. 79 



Kerner and Stahl have proved that tannin is distasteful to 

 snails, goats, rabbits, sheep, and cattle. It is therefore not strange 

 that natural selection has brought about the accumulation of this 

 disagreeable substance in organs and at stages of growth needing 

 special protection ; and, in fact, it is most abundant in young 

 leaves, flowers, and unripe fruits. 



Wigand has shown that red color often accompanies tannin, 

 and it is also true that red-leaved plants commonly contain oxalic 

 acid. Pick suggests that the union of elements of the oxalic acid 

 and of the red coloring matter, resulting in the formation of 

 crystals of calcium oxalate, prevents the formation of such an 

 excess of the acid as would prevent the action of the ferments by 

 which starch is made diffusible. Raphides are bundles of calcium 

 oxalate crystals. Stahl says that the single-pointed crystals 

 which exist in certain irises are an effectual protection against 

 snails, and that in the pickerel weed there are, besides these, 

 raphides and cells rich in tannin — perhaps a suggestion that 

 raphides may have arisen as the further development by natural 

 selection of such solitary crystals. For these delicate, sharp rods 

 are a formidable defense, piercing the skin of a would-be destroyer 

 of the tissues containing them like so many needles. (Taste Jack- 

 in-the-pulpit leaves.) 



So there is law in it all. Tannin abounds in plant-tissues. 

 Where it is, red color often appears ; and where there is red color, 

 oxalic acid is frequently found ; where oxalic acid is, raphides 

 may be formed ; and, finally, where there is tannin or raphides or 

 both, there are substances generally disliked by herbivora — a long 

 story, which the red color of the exposed parts of many plants 

 doubtless tells briefly but effectively to their enemies. 



For example, various members of the orpine family are not 

 eaten by large animals, because their leaf -tips — the most available 

 parts — contain tannin, " as shoivn by their dark-red color." Otto 

 Kunze says that the Javanese surround their coffee plantations 

 with a living hedge of red-leaved plants, so keeping off the swine, 

 which abhor this color. The brightly tinted leaves of young oaks, 

 maples, etc., are seldom eaten ; and in the tropics, where there is 

 the severest struggle for existence, gay leaves are most abundant. 



The mottled leaves of arum, lady's-thunib, some everlastings, 

 and prince's pine, and probably of adder's tongue and cyclamen, are 

 protected by raphides ; those of begonia have sour, and of coleus 

 and wild ginger, bitter sap. Such variegations of leaf-surface, 

 which may be imperceptible to the larger animals, may have much 

 significance to smaller ones. Species of caterpillars and of beetles 

 are often confined to particular orders or even genera of plants, 

 presumably because, like the cockatoo to the kanary nut, they 

 have adapted themselves to the peculiar characters of these plants, 



