ABNORMAL TISSUES. 



133 



buds and destroys their leading shoots and branches, but 

 lives on at the points of attack, forming globular swellings 

 in the wood that are quite sound, until the sporaphores of 

 the fungus break out and convert the swelling into a 

 canker. These knobbed saplings form valuable walking- 

 sticks and umbrella-handles. Similar knobs appear on oak 

 and sweet-chestnut saplings and are very common in oak 

 coppices on the Bagshot sands 

 in Surrey. Tr.] 



Damage by fungi, as in 

 witches' broom, cause abnor- 

 mal swellings in wood, which 

 usually are unsound and 

 detract greatly from its value. 

 Mistleto also (Fig. 50) causes 

 an abnormal swelling, and 

 eventually wood full of boles 

 on the trees which it attacks, 

 preferably apple-trees, pop- 

 lars, lime, silver-fir and white- 

 thorn. These cankers, etc., 

 are described fully in Vol. IV. 

 of this Manual on Forest 

 Protection. 



Swellings are produced 

 artificially by pruning sapl i 1 1 ^s 

 of dogwood, whitethorn, nsli 

 and oak, etc., in order to form 

 walking-sticks and umbrella- 

 handles ; mottled wood also by lopping ash-trees. More 

 experience is required as to the possibility of producing 

 healthy burrs artificially. 



Knottiness of Wood. The branching of a tree begins by 

 the budding of the pith of its leading shoot. Every subaerial 

 or subterranean branch (exeept adventitious shoots) is con- 

 nected by its pith with that of the leading shoot. In conifers 

 the branches are more or less in verticils, so that the distance 

 between two adjacent verticils gives the year's height-growth, 

 a) id the number of verticils gives the age of the tree down 



^Iver-tir wood injured \>\ 



mistleto. The li;iustori;i of the hitler 



;it!e im'diillary rays, in the 



tangential and radial sections of the 



wood. 



