CUP-SHAKE. 67 



and August, it will only do so at the expense of wood-forming 

 reserve-materials, and there may possibly result so complete a 

 check to the nutrition of the tree that the wood of one year may 

 fail to cohere to that of the preceding season, a cup-shake or ring- 

 shake being produced (Fig. 38). 



Such a separation between successive annual rings a defect 

 seriously interfering with the conversion of timber into planks 

 is, however, undoubtedly produced for the most part by various 

 other causes, and may be briefly here described. It occurs in 



FIG. 38. Cup and heart shake. 



various species, such as Hazel, Oak, Poplar, Pitch Pine, and Lignum 

 Vitse, and seems to some extent local. The oaks of Sicily, for 

 instance, a variety of our British species, Qutrcus Bdbur, and those 

 of the Forest of Dean (Q, Bdbur, var. sessilifldra) are peculiarly 

 subject to this defect, which in the latter case has been doubtfully 

 ascribed either to the rocky character of the soil or to the swaying 

 to and fro of the tall trees by strong winds. This action of wind 

 bending the rings of wood alternately in opposite directions, in a 

 manner obviously calculated to tear them apart, may well explain 

 the occurrence of this form of shake in Poplars. Cup-shake has 

 also been attributed to frost, the rings of sapwood and heartwood 

 in a living tree containing varying proportions of water and the 

 outer layers being most likely to freeze first. The explosive 



