ARTIFICIAL WOUNDS. 203 



Bruises. If a branch or woody stem is struck 

 sharply, with a hammer, for instance, the bruised 

 cortex, phloem and cambium are killed by the 

 blow, and the general effect is as if these tissues 

 had been removed at that spot by the knife, but 

 with the following complications. The bruised 

 cortical tissues rapidly dry as they perish, and may 

 adhere to the wood below. Consequently the still 

 sound parts bordering on the wound are not 

 released from pressure, but, on the contrary, have 

 to advance towards each other over the surface of 

 the wood under still greater pressures, in part due 

 to the tightening of the whole cortex as the dead 

 parts dry and contract, and in part due to the 

 above-mentioned adherence of the latter to the 

 wood. It results from this that such wounds heal 

 very slowly and badly, and when the killed patch 

 at last ruptures, wound-fungi, insects, and other 

 injurious agencies may get in and do irreparable 

 damage, as has been found to occur in cases 

 where such wounds have been made in striking 

 trees to shake down insects, fruit, etc. 



Notes to Chapter XXI. 



The essential facts regarding wounds and healing by 

 occlusion are given in Marshall Ward, Timber and some of 

 its Diseases, 1889, chapters viii. and ix., and in Laslett, 

 Timber and Titnber Trees, 1894, chapters iv. and v. More 

 detailed treatment will be found in Frank, Krankh. d. 

 Pflanzen, B. I. cap. 2, where the special literature is collected. 

 The reader may also consult Hartig, Diseases of Trees, Engl, 

 ed. 1894, pp. 225-269. 



