200 



PRUNING AND THINNING. 



PT. IV. 



to the head of tlie tree will form from its own deposit 

 an excrescence below it where it joins the stem, equiva- 

 lent to what are called ' the spurs,' or the ' swell of the 

 roots ' where they join the stem. De Candolle's obser- 

 vations would apply to roots as well as branches. But 

 if we bisect them lengthwise, we may see with a glance 

 that roots as well as branches stand on increasing, not 

 decreasing bases, where they join the stem. A dead 

 branch, or an undersized branch, overgrown by the 

 head of the tree, will cause a hollow below it, from 

 stopping the downward current from the head, which 

 cannot turn sufficiently short to deposit immediately 

 below the branch. This is often seen in beech-trees ; 

 and the groove is sometimes prolonged the whole extent 

 of the stem. 



Indeed, the unity of growth which must exist at the 

 foot of each branch, with the part of the stem which is 

 above it as well as below it, is apparent from the fact 

 that, when branches are cut off at the distance of an 

 inch or two from the stem, the descending sap of the 

 bark of the stem will ascend the bark of these stumps, 

 will well over between their dead upper bark and wood, 

 annually increase their girthing, and cicatrise or heal 

 over their ends, forming protuberances which will 

 occasion a consequent distortion of the grain of the 

 wood, and diversion of the current of sap. These pro- 

 tuberances will, indeed, in the course of time almost 

 entirely disappear, because, if equals are annually added 

 to unequals, in the course of time apparent, though not 



