148 THE PHYSIOLOGY OF PLANTS 



are of course useless for cutting into boards or planks. Lastly, 

 we come to a point which in practice is very rarely suffi- 

 ciently appreciated, namely, the sawing off of thick branches. 

 There are, of course, cases in which this procedure cannot be 

 avoided, as, for instance, in the removal of the crown for 

 purposes of grafting or after damage by wind or snow ; but 

 there are many occasions when this always somewhat dan- 

 gerous experiment might be, but is not avoided. This is 

 especially the case in putting up telegraph wires along wooded 

 roads and lanes and in thinning woods. 



The damages that ensue are of two kinds. First of all, 

 extensive wounds are made, which take years before they are 

 completely covered up, and during that time they give access 

 to wood-destroying Fungi. Secondly, the equilibrium of the 

 crown is disturbed in such a way that a sudden production of 

 numerous soft shoots takes place inside the crown, which 

 becomes choked and loses many of the horizontal fruit-bear- 

 ing branches. 



Some, who attach little importance to the removal of large 

 branches, argue that in woods such branches are often re- 

 moved to obtain straight trunks, and often decay away natu- 

 rally on account of the want of light, and in neither case does 

 the tree seem to suffer. 



But in both cases the argument falls to the ground. For 

 in the practice of forestry the removal of branches for the 

 benefit of the main stem often induces the decay of the tree, 

 and in the case of branches breaking off for want of light, the 

 branch is dead before separation takes place, and the cells and 

 vessels are sealed up with plugs of gum, resin, and by thylloses, 

 and are rendered unfit for fungal growths. 



Of course the trees vary very much with regard to their 

 powers of resisting any such injury. For while in Conifers 

 the wound is covered up with resin and the stump of the 

 branch becomes soaked with resinous oils, which defy fungal 

 attacks, this is not the case with most Dicotyledons. In our 

 fruit-trees, a wound of two or three inches in diameter, which 

 becomes covered in in from six to eight years, always causes 

 brown spots of injured tissues in the stem. With larger 

 wounds this is still more the case. Decay will then almost 



