!V.] CUP-SHAKE: RING-SHAKE. 59 



almost invariably either frost or sun-durn, and it is usually- 

 possible to determine which by paying attention to the 

 conditions. 



The plane followed by the crack is that of the 

 medullary rays, and the separation of the wood is due 

 to its violent contractions, or shrinkage, and expansions 

 during the process of rapid freezing from without in- 

 wards. In other cases, especially with smooth-stemmed 

 trees such as the Beech and Hornbeam, the sun's rays 

 kill the living tissues of the cortex, and longitudinal 

 cracks result in the wood. Occasionally both frost and 

 insolation are concerned. 



It occasionally happens that defects of the nature of 

 " cup-shake "are traceable to the base of the tree having 

 been scorched by a forest fire. The cambium is then 

 so baked on one side of the tree (or even nearly all 

 round) that it is many years before the still living 

 portions of the cambium can entirely cover over the 

 dead parts, and the consequence is the production of a 

 series of more or less irregular occluding layers* super- 

 posed over the hitherto regular and concentric annual 

 rings. As the occlusion approaches completion, the 

 burnt side of the tree shows external ridges and defects 

 very like those due to sun-cracks or frost-cracks. 



The cup-shake or ring-shake (Figs. 12'a and i>). This 

 shake, which is most frequently met with near the roots 

 of trees, consists of a cavity or separation of two of the 

 concentric layers, often accompanied by more or less 

 traces of rot, if the injury is of long standing. This 

 deficiency of cohesion between the woody layers is 

 supposed to result from sudden changes of temperature, 

 from the roots passing through a peculiar vein of soil, 



* J.e, the subsequently developed annual layers of wood which gradually 

 cover over (occlude) the injured part. 



