182 THE GYPSY MOTH. 



increased productiveness of our cultivated plants, such a slight 

 weakening may be overlooked, if any other special advantage is 

 gained.* 



Tarring the wounds gives the most satisfactory result when 

 pruning is done late in the autumn or in winter, for it is 

 then that the tar is best absorbed by the surface of the 

 wound. When branches are cut off in spring or summer, 

 the tar fails to penetrate the surface of the wound because 

 of the flowing sap, and its thin superficial layer does not 

 prevent the cut from drying later. In drying, cracks are 

 formed, into which water and the spores of fungi may gain 

 entrance. For this reason it is often necessary to apply two 

 or more coats of tar to the wound. 



Having considered some of the objections to removing 

 limbs in summer, it is plain that the late winter is the most 

 favorable time for such pruning as is here advocated. There 

 is then less exposure to extreme cold to be considered. It 

 is known that certain trees have a considerable flow of sap 

 in winter. It is said that the Indians were accustomed to 

 draw the sap from the sugar maples in November, when 

 good sap days frequently occur, f It may be better to prune 

 such trees in the spring or summer. The results of pruning 

 native deciduous and coniferous trees at different seasons 

 of the year have never been fully observed with scientific 

 accuracy, and there is much to be learned. 



Removal of Dead or BroTcen Branches, — Dead branches 

 may be removed at any time of the year, if proper precau- 

 tions are taken to avoid injuring the bark or trunk of the 

 tree in the operation. If these branches are left upon the 

 tree until they decay and drop off or are torn away b}^ 

 the winds, the bark loosens and forms a harboring place for 

 the gypsy moth and certain other insects, which hide beneath 

 it and oviposit there. Their eggs being out of sight, they 

 hibernate in comparative safety until the following spring, 

 when the larv?e hatch and attack the foliage, thus weakening 

 the tree. If dead branches are not removed, they are some- 



* "A popular treatise on the physiology of plants," by Dr. Paul Sorauer. English 

 edition by Prof. F. E. Weiss, pages 137, 138. 



t "The Circulation of Sap in Plants," by W. S. Clark. Annual Report of the 

 Massachusetts State Board of Agriculture, 1873-74, page 162. 



