the true Sap of Trees is deposited during Winter. 91 
from taste ; but when obtained at a greater height, it was 
sensibly sweet. The shortness of the trunks of the sycamore 
trees, which were the subjects of my experiments, did not 
permit me to extract the sap at a greater elevation than seven 
feet, except in one instance, and in that, at twelve feet from 
the ground, I obtained a very sweet fluid, whose specific gra- 
vity was 1.012. 
I conceived it probable, that if the sap in the preceding cases 
derived any considerable portion of its increased specific gra- 
vity from matter previously existing in the alburnum, I should 
find some diminution of its weight, when it had continued to 
flow some days from the same incision, because the alburnum in 
the vicinity of that incision would, under such circumstances, 
have become in some degree exhausted : and on comparing 
the specific gravity of the sap which had flowed from a recent 
and an old incision, I found that from the old to be reduced to 
1.002, and that from the recent one to remain 1.004, as in the 
preceding cases, the incision being made close to the ground. 
Wherever extracted, whether close to the ground, or at some 
distance from it, the sap always appeared to contain a large 
portion of air. 
In the experiments to discover the variation in the specific 
gravity of the alburnum of trees at different seasons, some 
obstacles to the attainment of any very accurate results pre- 
sented themselves. The wood of different trees of the same 
species, and growing in the same soil, or that taken from 
different parts of the same tree, possesses different degrees of 
solidity ; and the weight of every part of the alburnum ap- 
pears to increase with its age, the external layers being the 
lightest. The solidity of wood varies also with the greater -or. 
N a 
