84 THE PHYSIOLOGY OF PLANTS 



and we ought therefore to leave the ends of all the branches 

 intact, i.e., we ought not to prune at all. But opposed to 

 this requirement is the necessity to reduce the whole system 

 of branches to a certain extent, as otherwise, in the course of 

 the summer, some branches would die, because the damaged 

 root system is not able to supply all the water which would 

 be needed by the entire system of branches. But often those 

 branches which die off are just those which are most essential 

 for a regular growth of the crown, and therefore are an irre- 

 parable loss to the tree. Both requirements must therefore be 

 taken into consideration, and this is done by leaving intact 

 some branches which are essential for the formation of a good 

 crown, and reducing the intervening branches to one-half or 

 one-third of their length, according to the amount of damage 

 of the root system. In this way we secure the development 

 of a number of leaves at the ordinary time, and consequently a 

 certain amount of new assimilated food substance. For these 

 few branches the amount of sap absorbed is quite sufficient, 

 and the development of adventitious roots begins near the cut 

 ends of the rootlets before the buds of the pruned branches, 

 which only form a small amount of leaf surface, have begun 

 to open. The absorptive organs will therefore have increased 

 in proportion to the new leaf surface. 



The present method is to cut back all the strong branches, 

 and to confine the production of leaves to the lower, lesa 

 vigorous, and later developing buds. Consequently, the un- 

 folding of the leaves takes place at a later and hotter period, 

 when the leaves will remain smaller, but in spite of that will 

 require more water for their transpiration. 



The first-mentioned method of "partial pruning" deserves 

 the preference for transplanted trees and bushes. 



It is of course taken for granted that the larger cut sur- 

 faces will be covered with tar or wax, and that the stem& 

 themselves will, if necessary, be protected from evaporation by 

 a covering of moss or straw. 



