246 PLANT RELATIONS. 



The red shades, however, do not seem to hold any such 

 relation to the disorganization of chlorophyll. The red 

 coloring matter appears as a stain in the cell sap, so that 

 what might he called the atmosphere of the active cell is 

 suffused with red. Certain experiments upon plant colors 

 have indicated that the presence of the red color slightly 

 increases the temperature by absorbing more heat. This 

 has suggested that the red color may be a slight protec- 

 tion to the living substance, which has ceased working 

 and which is in danger of exposure to cold. If this be 

 true, it may be that the same explanation will cover the 

 case of the red flush so conspicuous in buds and young 

 leaves in the early spring. It must not be supposed that 

 the need of protection has developed the color, but that 

 since it is developed it may be of some such service to the 

 plant. The whole subject, however, is too indefinite and 

 obscure to be presented in any other form than as a bare 

 suggestion. 



Even the conditions which determine autumnal colora- 

 tion have not been made out certainly. To many the au- 

 tumnal coloration is associated with the coming of frost, 

 which simply means a reduction of temperature ; others 

 associate it with diminishing water supply; still others 

 associate it with the change in the direction of the rays of 

 light, which are mora oblique in autumn than during the 

 active growing season. It is certainly true that the colors 

 are far more brilliant in certain years than in others, and 

 that the coloration must be connected in some way with 

 the food relations of the plants. Eecent experiments have 

 shown that the red coloration is largely dependent upon low 

 temperature, which affects certain of the food-stuffs, and 

 the red stain is one of the products. 



The autumnal colors are notably striking in American 

 forests on account of the fact that in these forests there is 

 the greatest display of species, and hence not only are more 

 colors produced, but they are usually strikingly associated. 



