LEAVES IN SEASONS 161 



and as a consequence are very readily broken 

 down when exposed to the sunlight. In the 

 living normal leaf the green color forms a most 

 effectual shield from the effects of the rays, 

 but when the retreat is begun, one of the first 

 steps results in the disintegration of the chlor- 

 ophyll. This would allow the fierce rays of 

 the September sun to strike directly through 

 the broad expanses of the leaf, destroying all ^°^f^ ^ ^ P*"®" 

 within, were not other means provided for ^^ mg screen 

 protection. In the first place, when the 

 chlorophyll breaks down, cyanophyll (blue- 

 green) is formed, anthocyan (blue-red) is 

 constructed by the protoplasm, and at the 

 same time the yellow lipochromes present in 

 the cells, chiefly xanthophyll, become visible 

 and take a share in protecting the plastic sub- 

 stances, which absorb the sun's rays in the 

 same manner as the chlorophyll, so that the 

 leaf exhibits outwardly a gorgeous panoply 

 of color in reds, yellow, and bronzes that 

 makes up the autumnal display. From the 

 wild riot of tints shown by a clump of trees 

 or shrubs, the erroneous impression might be 

 gained that the colors are accidental in their 

 occurrence. This is far from the case, however. 

 The key-note of color in any species is con- 

 stant, with minor and local variations. The 

 birches are a golden yellow, oaks vary through 

 yellow-orange to reddish brown, the red maple 



