'JIIH MOXIHI.Y BULLKTIN'. 



83 



holding in solution mineral elements from the soil, thus elaborating 

 true or complete plant food to be distributed throughout the system 

 between the bark and the wood. The conditions for leaf action are the 

 presence of grains of green coloring matter in the cellular tissue of the 

 leaf, technically, chlorophyll, and the light of the un. In the dense 



I- IG. 18. — Orange tree headed low and showing the crowded condition of the 

 inner branches. These should be thinned out so that sunlight can enter 

 the center of the tree. (Photo by A. D. Shamel.) 



shade of the trees, and in the darkness of night, the conversion of plant 

 food material into plant food fitted to build the structure of the tree, 

 does not take place. 



If the foliage is yellow and there are chlorophyll grains only in the 

 veins of the leaves, it is inefficient to digest raw material into nourish- 



ing food 



4—1552 



Thus it is plain that tree life is at a low stage; plain, too, 



