44 The Living Plant 



theory, that of the protective and heating screen, requires in 

 autumn leaves certain features which the spring coloration does 

 in fact to some extent exhibit, viz., a prevalence of red rather 

 than yellow, a fairly uniform coloration over all the parts to be 

 protected or warmed, an especially deep coloration in the conduct- 

 ing parts, and a fairly constant development of the color year after 

 year without much regard to the details of the weather. As a 

 matter of fact the phenomena of autumn coloration are differ- 

 ent at almost every point red is less common than yellow; the 

 colors are very uneven in distribution, forming spots, blotches, 

 and streaks; the color shows no particular tendency to cover the 

 conducting veins: and its intensity varies greatly in different 

 years, even almost to suppression of red in certain kinds of leaves 

 in some seasons. The utility theory of autumn coloration re- 

 ceives, therefore, no support from comparison with spring color- 

 ation, even granting, as is not at all certain, that the latter is 

 useful. The facts, therefore, taken all together seem to favor 

 the incidental theory, which may thus be expressed ; that autumn 

 coloration, for the most part at least, is a purely incidental result 

 of the chemical and physical conditions which happen to prevail 

 in ripening leaves and around them, and has in it no more element 

 of utility than has the red of a sunset or the blue of the firmament. 

 The yellow and red in the autumn coloration are so much more 

 common and striking than any other colors that they naturally 

 attract the most of our attention. Yet other colors occur, as 

 everybody knows well, and as appears very clearly on the accom- 

 panying plates (Plates II, III), which represent a selection from 

 New England autumn vegetation, photographed in the natural 

 colors. In fact, however, the great variegation thus displayed 

 results from permutations and combinations of a very few colors. 

 In addition to the red and yellow, there is only one other pigment 

 at all common in autumn leaves, and that is an occasional brown, 

 the mode of formation of which is uncertain. Most of the brown 

 color in such leaves, however, belongs to the cell-walls, which are 



