164 MASS. EXPERIMENT STATION BULLETIN 170. 



There is a difference of opinion as to the best time to prune, some 

 authorities advocating spring and others preferring the fall of the year. 

 Many people prune when the tree is in foliage, — in May or later. There 

 are advantages in pruning in either season. Since trees occasionally bleed 

 when pruned in early summer, painting the wounds is not always success- 

 fully accomplished under these conditions; on the other hand, scars on 

 vigorous trees are likely to heal somewhat during the summer if the 

 pruning is done early. 



The tools required in pruning are as follows: for general work, a good 

 coarse-tooth, wide-set saw (5 teeth per inch) ; for larger limbs, a small 3 

 or 4 foot hand cross-cut saw; and for smaller limbs not easily accessible, 

 a pole saw is convenient. Pole-saw blades may be ordered through hard- 

 ware dealers, and may be fitted to poles of any desired length. A pole 

 hook, wliich can be made by any blacksmith, is often useful for removing 

 the small dead branches. For lowering large Hmbs a set of blocks is 

 necessary, and in the felling of trees a cross-cut saw is indispensable . Ropes 

 of various sizes, iron wedges for felling trees, axes, mallets and chisels, 

 ladders, spurs for climbing, etc., are also indispensable. 



The above are the most essential tools for pruning shade trees, although 

 there are others which are extremely useful and time saving. 



Healing of Wounds. 



A protective feature characteristic of all plants is well illustrated in the 

 healing of wounds. The healing tissues (callus) in a tree are the cambium 



and adjacent meristematic cells located be- 

 tween the wood and the outer bark. The 

 plastic substances which provide the material 

 for growth and healing are manufactured in 

 the leaf, and are transferred through certain 

 tissues of the inner bark (pliloem) adjacent 

 to the cambium to various parts of the tree. 

 When the tree is girdled or the bark removed 

 no growth takes place below the girdling be- 

 cause the channels of transportation are 

 destroyed. 



In some young plants the pith cells possess 

 the power to form a callus, but such cases 

 are rare and of little importance. The 

 younger the tissue or organ the more quickly 

 it will heal, providing other tilings are favor- 

 able, and vigorous trees will form a callus 

 much more quickly than old or weak ones. 

 Since the plastic substances are manufac- 



FiG. 25. — Healing of wound, tured in the leaf, and since it is these sub- 

 Most active healing follows glances which are necessary for the develop- 



most direct lines of trans- . . , 



ference of plastic materials, ment of healmg tissue, it IS Only when 



