ARTIFICIAL WOUNDS. 201 



sides of the wound than above and below, owine 

 to differences in the distribution of the nutrient 

 materials. 



Stool-stumps. When a tree is felled, the stump 

 may, if the section is close to the ground and kept 

 moist, begin to form a thick rim-like callus round 

 the wood, in which adventitious buds soon make 

 their appearance, and grow out into so-called 

 Stool-shoots. The products of assimilation of these, 

 and the stores accumulated in the stump, often 

 suffice to feed the callus sufficiently to enable it to 

 grow over and completely occlude the wound, if the 

 wood surface is not too large, or so long exposed 

 that rotting processes have meanwhile set in. 



Ringing. If the strip of cortical tissues and 

 cambium is removed all round the stem, exposing 

 the wood in a form of a ring, complications may 

 ensue owing to the following circumstances. A 

 well-marked callus appears at the upper edge of 

 the wound, because, the transpiration current up 

 the young wood not being stopped, plenty of 

 water and salts from the soil can reach the leaves; 

 but the nutritive materials supplied by the latter 

 are accumulated at the upper lip of the wound 

 owing to the stoppage there of their descent in 

 the phloem, cortex, etc. No such callus-lip 

 appears at the lower margin of the wound owing 

 to want of these supplies. Consequently the 

 occlusion and healing of the ring-wound only 

 takes place from above downwards, and if the 

 ring of cortical tissues removed is a broad one, the 

 healing may be a long process, or may even be 



