52 LIFE OF A TREE, 
cellular system (or pith) of the stem takes place, 
and each bud sends down ligneous matter within 
the bark and above the wood of the shoot from 
which it sprang; thus forming on the one hand 
a new layer of wood, and on the other a fresh 
deposit of bark.” 
We thus see, that the following distinct phe- 
nomena may be recognised in this portion of the 
history of a tree: the expansion and functions 
of its leaves, the flow of its juices, and the for- 
mation of cellular and woody tissue. It will be 
convenient to speak of the flow of the vegetable 
juices, previously to our mentioning some par- 
ticulars respecting the other phenomena. 
If in an early summer-day a notch is made 
with a knife into the stem of a healthy succulent 
plant, immediately it is seen to bleed, pouring 
forth a clear, somewhat viscid fluid. If now the 
notch is made deeper and wider, we can see from 
which portion of the stem the fluid runs; anda 
little examination will shew us that it is from the 
stem below, and not from that above the cut that 
it chiefly proceeds. We learn from this, that the 
motion of the sap, for that is the proper name of the 
fluid, is very strongly in the direction from below 
