SEASON FOR PRUNING. 181 



An examination of injurious results of spring and summer 

 pruning indicates that the injury sometimes extends down- 

 ward and serious harm is done. 



There is a danger from the running of sap which occurs 

 when pruning is done in spring or summer, aside from any 

 possible harm resulting from the drain on the vitality of the 

 tree. Warmth and dampness are particularly favorable for 

 the germination of parasitic fungi and the progress of decay. 

 Though decay may occur without the presence of these 

 organisms, its progress is more rapid when they are pres- 

 ent. Therefore, wounds which are constantly kept wet in 

 warm weather by the flow of crude sap are most likely to 

 decay. 



There are reasons also why pruning in summer is likely 

 to be weakening to the tree : — 



If the term, winter pruning, is given to any removal of shoots 

 during the resting period of a woody plant, we may say generally 

 that winter pruning is strengthening, while summer pruning is 

 weakening. 



If any portion of the shoot system is taken away after it has 

 passed through one summer, the structure and activity of the 

 root system — that is, its power of absorption and of forcing up 

 water — is such that it can nourish all the branches. At the 

 beginning of the next period of activity, by cutting away some 

 branches the water-consuming area is diminished. The same 

 amount of pressure has therefore a reduced field of action, 

 and consequently the effect on the remaining branches must be 

 increased. 



By pruning in the summer we remove soft shoots with only 

 recently developed leaves. The latter have yet their chief work 

 to perform ; for at the commencement they are developed at the 

 cost of the reserve material which is stored up in the branch, then 

 comes a period at which the young leaf requires all the substance 

 it assimilates from without for its own growth, and only after 

 its full development does it begin to work for the benefit of 

 the branch. If, therefore, a soft shoot is taken away, the older 

 portions of the branch are robbed of the materials which Avere 

 used in the unfolding of the leaves, without receiving anything in 

 return from the leaves they have developed. This causes, there- 

 fore, a loss to the general economy of the plant ; but, with the 



