36 



BULLETIN 1490, U. S. DEPARTMENT OF AGRICULTURE 



OTHER TYPES OF DEFECTS 



Other common defects — ring distortions, pitch pockets, gum spots, 

 black check, staining, and pith flecks — are often caused by insects 

 or associated with insect attack. Such defects, however, are not al- 

 ways necessarily caused 

 by insects. 



DEFECTS CLASSED AS RING 

 DISTORTIONS 



Characteristic distor- 

 tions and abnormalities 

 in the annual rings of 

 trees result from defolia- 

 tion by leaf-feeding in- 

 sects, as well as from 

 other causes, as pointed 

 out by Hartig, Harper, 

 and Craighead (48). De- 

 struction of the leaves 

 at certain periods causes 

 a reduction in the normal 

 amount of food manu- 

 factured by the tree, 

 with consequent loss in 

 the amount of wood laid 

 on and the formation of 

 incomplete annual lay- 

 ers or double rings 

 ( false rings ) . Many 

 species of trees are 

 subject to defoliation, 

 though little is known 

 of the resulting effects 

 except in a few cases. 



Larch, fir, spruce, 

 jack pine, lodgepole 

 pine, western yellow 

 and white pines, hem- 

 lock, oak, hickory, ca- 

 talpa, birch, and cherry 

 are some of the trees 



Fig. 39. — A and B, two views showing small "pitch subject to frequent Or 



%%&£.£fi$\8?" eausea by ' arra ° f a flJ ' periodic defoliation. 



RING DISTORTIONS CAUSED BY DEFOLIATION BY THE BUD WORM 



Defoliation by the bud worm 29 on spruce and fir produces the 

 first year a decided decrease in wood on the upper stem, while an 

 abnormally larger ring is laid on at the base. In subsequent years 

 a gradual reduction occurs, the narrowest ring being laid on some 

 four or five years later throughout the tree. Gradual increase then 



29 Cacoecia (Harmologa) fumiferana Clemens. 



