242 PLANT RELATIONS. 



The two colors hold a very diiJerent relation in the leaf 

 cell. It is known that the yellow is due to the break- 

 ing down of chlorophyll, so that the chloroplasts, which 

 are green when active, become yellow when disorganizing, 

 and finally bleach out entirely. That yellow may indicate 

 a post mortem change of chlorophyll may be noticed in con- 

 nection with the blanching of celery, in which the leaves 

 and upper part of the stem may be green, the green may 

 shade gradually into yellow, and finally into the pure 

 white of complete blanching. 



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 be 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 th(^ 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 I'eduction of temperature ; others 

 associate it Avith diminishing water supply ; still others 

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

 light, which are more oblique in autumn than during the 

 active growing season. It is certainly true that the colors 



