LUTHER BURBANK 



It is not as well known as it should be to gar- 

 deners and orchardists that the leaves of a plant 

 are the seat of the essential laboratory in which 

 hydrogen and oxygen and carbon are compounded 

 to make living matter, and that the leaf system 

 of tree or shrub is directly responsible for the 

 growth of the root system. The protoplasm and 

 starch and woody fiber that go to make up the 

 root and enable it to grow and extend its ramifi- 

 cations are first compounded in the leaves, and 

 are sent down through the cells of the cambium 

 layer of the bark in return for the watery sap that 

 the root system collects as raw material and sends 

 up for compounding in the wonderful leaf labo- 

 ratories. 



There is, in short, the closest interdependence 

 between leaf system and root system in the case 

 of every plant; and this is strikingly shown by 

 observation of trees and shrubs. If a tree has a 

 healthy leaf system you may be sure that it has a 

 good root system. 



We have noted in the case of the walnuts how 

 an inherently vigorous root system of a hybrid 

 variety may stimulate the development of the leaf 

 and branch system. An opposite illustration of 

 the co-operation between branch and root is given 

 when a very vigorous scion is grafted on relatively 

 weak roots. Here the vigor of the top may give 

 such stimulus to the root system that it keeps pace 

 with the growth of the visible parts of the tree, 

 far surpassing the limits it would have attained 



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