54: LIFE OF A TREE, 
is from below; and we thus gather the important 
fact, that sap vises through the wood, and descends 
between the wood and the bark, and through the 
inner portions of the bark also. Beginning from 
the roots, we may trace its circulation through 
the tree in the following manner. A_ heavy 
shower of rain falls, and fills the soil with mois- 
ture: as it filters downward it dissolves many 
ingredients which it meets with in the earth, and 
coming at length into contact with the delicate 
roots, it is drunk in by them, and so enters the 
system of the plant. Immediately it begins to 
move upwards; passing along the roots it enters 
the stem, ascends through the woody tissue, enters 
the leaves, is there exposed to the light and air, 
thence descends again through the bark, and 
reaching the roots is discharged, having fulfilled 
all the duties required of it, to give place to 
the continually in-pouring stream which goes 
through the same career. 
The force with which this circulation takes 
place is very surprising. By taking a young 
growing branch of a tree, and fitting one end 
of it into a glass tube, and by means of a little 
cement making the joint perfectly tight, we shall 
