Chap. II.] 
COURSE OF THE SAP. 
45 
the same thing in cutting down some poplar- 
trees in France. I afterwards satisfied myself, 
in various ways, that the whole of the wood is 
the conduit for the upward course of the sap. 
In April, 1832, I found a birch-tree in Dyr- 
rham Park, of from sixty to seventy years’ 
growth, which had a large scar from injuries 
from cart-wheels. The scar might have existed 
from fifteen to thirty years, being perfectly in¬ 
durated, and in parts turned to touchwood. I 
tapped the scar in the centre with a very large 
gimlet. I had not pierced an inch before it ran 
freely while boring. I bored about three inches 
in depth. The tree was about nine inches 
through, in the direction of the bore. The dead 
surface-wood was perhaps a little more than a 
quarter of an inch in depth. The dropping was 
so frequent as almost to amount to a stream. 
This could only have flowed from the heart- 
wood; since no alburnum, or new wood, had 
been deposited on the scar for about twenty 
years. 
It is stated that Coulon accidentally observed 
the sap flowing in the heart-wood, in felling 
some poplar trees, as I believe, about 1830. His 
farther proof of boring with an augur, in my 
opinion, goes for nothing. As the augur must 
The upward sap 
goes through 
the heart-wood; 
proof by expe¬ 
riment. 
