60 



heart wood than other parts of the same 

 rings, so that on the same transverse 

 section of a tree there shall be more rings 

 of sap wood on one side than on the other. 

 This may be observed in oaks ; but on the 

 scar of this tree no alburnum or sap wood 

 has been deposited for upwards of thirty 

 years. 



As the roots of trees grow in length 

 through the earth they are in perfect con- 

 tact with it, and as they increase each 

 year in girthing or diameter this contact 

 is continued, and the pressure against the 

 earth even increased. 1 imagine that this 

 close contact of the roots with the earth 

 is very essential for the absorption of 

 moisture ; and that when a ball of earth 

 is taken up with a transplanted tree, the 

 parts of the roots contained in the ball 

 are infinitely more efficient for the supply 

 of sap than five times their length of root 

 not in perfect contact with the earth. 

 But certain it is, that, by taking a large 



