THE FLOWER AND THE BEE 



anthocyanin soon appeared in the upper side of the leaves, while 

 leaves of plants in control experiments j^laced in pure water 

 remained green. Water-plants, like Hydrocharis, placed in a 

 sugar -solution also developed red coloring in the leaves in a 

 few days. When Overton removed his plant-cultures to the 

 shade, the red coloring quickly disappeared, but again re- 

 turned when they were exposed to bright light. Leaves, 

 flowers, and fruits frequently display red coloring on the side 

 exposed to direct sunlight, while the side in the shade remains 

 green. During the summer the leaves of plants in the Alps 

 are much oftener red-colored than in the lowlands, because the 

 night temperature is lower and the light-intensity higher. Ker- 

 ner found that the anthocyanin in plants grown in an Alpine 

 garden at an elevation of 2,195 metres above the level of the 

 sea was brighter-colored and more abundant than in the botani- 

 cal garden at Vienna. The glumes of grasses, the leaves of 

 stonecrops, and the pure-white petals of some flowers became 

 red or purplish red. Winter leaves become red-colored be- 

 cause a lower temperature causes the sugar content to be in- 

 creased at the cost of the starch. 



While some ecologists regard anthocyanin as merely a by- 

 product of the chemical activities of the cell, others, as Stahl, 

 think that its role is the absorption of heat. When leaves con- 

 taining anthocyanin were placed in a vessel of water the tem- 

 perature of the water was raised 4 degrees higher than that of 

 an equal quantity of water containing green leaves of the same 

 superficial area, both vessels being placed in the sunlight. It 

 is readily conceivable that in early spring, when the temperature 

 of the air is near the freezing-point, this additional heat might 

 be a great advantage. Red coloring is seldom common in 

 foliage containing much yellow pigment, consequently antho- 

 cyanin is rare in the birches, which have yellow leaves in spring 



246 



