132 PROPERTIES OF WOOD. 



brackets, etc. Large burrs are generally unsound internally, 



and are then less valuable than the smaller ones ; they often 



bear epicormic twigs. 



[Mathey states that burrs from Corylus colurna, the tree- 



hazel of the Levant and Himalayas, are much used by 



cabinet-makers, and so were excrescences on the rootstock 



of Callitris quadrivalvis, in 



[^7 ~>% Algiers. These latter burrs 



are produced by grazing and 

 fires, and were highly prized 

 for their beauty by cabinet- 

 makers, but as they have 

 become extremely rare and it 

 is desired to preserve the tree, 

 they are no longer obtainable ; 

 probably the origin of the 

 Levant hazel burrs is due to 

 similar bad usage. Some- 

 times, as in beech, the dor- 

 mant buds are separated from 

 jV'\ the pith by the woody growth, 



but grow in the living cortex, 

 and form little round excre- 

 scences, projecting from the 

 bark, being termed sphaero- 

 blasts. They are quite use- 



^MBLL^_-.J-^.:--__i: ______ iiil less. 



Fig. 49.-Bircl's-eye maple. From the . The reason for the f rm a- 

 sugar-maple. The bird's eyes are shown tion of buiTS Oil trees is Said 



as transverse sections of the dormant by Mayr to be un l mown . 



shoots. The lower part of the plate is , ,, . 



a radial section, shown lengthwise. dentl y m man .Y cag es they are 



due to injuries when the trees 



were young, so that dormant buds low down the stem grew at 

 the expense of the latter, and not being able to develop into 

 ordinary branches owing to repeated injuries, or to their 

 position deprived of sufficient light low down on the stem, they 

 produced masses of contorted tissue. 



A fungus (Dothiora sphacroides) growing on ash saplings, 

 both seedlings and coppice-shoots, sometimes attacks their 



