COURSE OF THE SAP. 



PT. II. 



year by the length of the new shoot of the branches 

 and roots. 



The shake, The medullarv rays and the concentrical piths are 



and cup- J. 



shake. go far distinct from the wood, that what are absurdly 

 called, and commonly believed to be, shakes arise in 

 them. All the shakes which I have observed show on 

 each side of the tree, from which I imagine they must 

 be the result of disease in the original medullary rays 

 of the seedling : for one can scarcely suppose sym- 

 pathy between two oj)posite new medullary rays which 

 have no junction with each other ; nor would one 

 have anticipated this in two opjDosite original rays. 

 That the shakes pass through the bark shows, I think, 

 that the rays of the wood communicate with those of 

 the bark. These shakes often rise to a great height, 

 and are never cured. A diseased concentric pith is 

 called a cup-shake. 



The concentric pith or cup-shake, may be called 

 finite ; the medullary ray shake, infinite, by com- 

 parison : that is, a cup-shake is conical, and cannot 

 extend above the cone of the year's growth in which 

 it is generated. All the timber, therefore, which is 

 above that cone, or outside it, is sound. The medul- 

 lary ray shake may be continually prolonged upward, 

 downward, and outward and inward, with the growth 

 of the tree. 



The new medullary rays proceeding from the new 

 rings of pith may be easily seen in oaks : and I think 

 that the medullary rays may be seen to prolong them- 



