66 



Further. Knots not only retard the 

 growth of timber, in the ways just men- 

 tioned, but also by obstructing the sap. 

 — A little reflection must convince us, 

 that it is impossible, either plant or ani- 

 mal, whose juices are obstructed, can ad- 

 vance as fast in size, as one which has free 

 circulation. 



Where the timber is knotty, the grain 

 or veins both of the w ood and bark are 

 found curvins; in different directions. 

 This, however, w^ould do little harm to 

 the ascent of the sap, were it not that it 

 occasions a contraction in the vessels. — 

 If the grain be finer, the sap-vessels must 

 of course be smaller. — We may be cer^ 

 tain of the fact, though we cannot see 

 them. 



It is true, that while a tree is young and 

 vigorous, (which is in effect saying, while 

 it has a plentiful supply of sap,) its quan- 

 tity may be such, as to act with a force 



