52 
COURSE OF THE SAP. 
[Part It. 
merary watery parts necessary to take up from 
the soil and conduct to their destination the car¬ 
bonic acid, ammonia, and inorganic matters 
requisite for vegetable life, and that it exhales 
the unnecessary gases, &c. after the decomposi¬ 
tion of the constituents absorbed from the soil. 
And is not the great accumulation of ash, or 
incombustible or inorganic matter, found in the 
leaf, as compared with that found in the wood, 
an argument that the leaf is the organ of excre¬ 
tion ? The quantity of ashes or inorganic matter 
left by the leaves when burnt is perhaps from 
twelve hundred to two thousand per cent, greater 
than is left by the wood, that is, it is from 
twelve to twenty times as much. And it is 
possibly on this account that these organs of 
excretion are themselves excreted. The division 
of trees into deciduous and non-deciduous is not 
strictly correct. All are deciduous; that is, 
all defoliate or lose their leaves,—those which 
we call deciduous generally in about six months, 
those which we call evergreens generally in about 
twelve months. Evergreen trees, however, differ 
in time, but each has its fixed period for defo¬ 
liation. 
Certainly the transpiration or giving off of 
water from the leaf, when exposed to drought, 
