SAP ACTION. 
FRED. A. WATT. 
N order to understand this subject 
we must first ascertain the condi- 
tions under which sap is first pro- 
duced, what it is, and how it circu- 
lates. 
To do this we must first know some- 
thing of the structure of those parts of 
the tree which serve as channels, or 
ducts, and those other parts which 
gather the sap and dispose of the waste 
after it has completed its mission. 
To begin with, the tree is composed 
of small structures, too small for the 
naked eye to distinguish. Each struc- 
ture is, at least for atime, a whole in 
itself, containing solid, semi-solid, and 
fluid parts which differ in their chemical 
nature. These structures are the cells, 
and when a large number of them are 
united in close contact they form a cel- 
lular tissue through which the sap 
passes from the roots to the leaves, and 
from the leaves to the growing parts 
of the young tree, or shoot. 
This cellular tissue is superseded by 
another tissue which is much stronger 
and which takes up the work of the | 
cellular tissue, when the tree becomes | 
too large to be supported by the weaker 
form. It is more solidly formed and is 
composed of elongated cells which are 
joined together in a series with their 
ends overlapping. This is known as 
woody fiber. The cellular tissue now 
exists in the tree stem only in the pith, 
and in the medullary rays which we 
may see in the grain of any hard wood, | 
radiating from the pith. 
With the statement, then, that these 
tissues form the timber, and that the 
bark and roots only present a modifica- 
tion of the same structures, we will 
pass to the tree as we see it with the 
naked eye. 
If we saw the trunk of a tree, of any 
considerable size, squarely in two, we 
find three forms which differ in solidity, 
rigidity, and appearance; namely, the | 
heart-wood, sap-wood, and bark. The 
heart-wood is the firm, solid wood sur- 
rounding the center of the tree, athe 
the heart-wood, while the bark forms 
the skin or outer covering for the 
whole. 
Trees grow from the center outward, 
hence the present sap-wood will in 
time become heart-wood and be cov- 
ered by a new layer of sap-wood, and 
the present heart-wood is simply sap- 
wood which has become solidified by 
the deposit within its tissues of resin- 
ous and other matter secreted by the 
tree. It is now useless for sap-carrying 
purposes and seems to exercise only 
the function of supporting the tree in 
its position. It is through the outer, 
younger layer or sap-wood that the 
sap ascends. 
Now, if we examine the end of our 
stick more closely we see a series of 
rings, clearly marked, circling from 
the center of the tree and ranging in 
size from the tiny one which encloses 
the pith, to the large one which forms 
the outer surface next to the bark. 
They are caused by a constant annual 
deposit and outward growth, by which 
a layer is added to the outer surface of 
the sap-wood each season. Hence, by 
counting these we may determine the 
age of the tree. Less distinct rings 
may appear but they will not deceive 
us as we know that they are caused by 
a cessation of growth, which may have 
been caused by drouth. 
As a general rule these rings are 
more distinct in trees inhabiting a 
climate where vegetation is entirely 
suspended by the cold after each layer 
is formed. In warmer regions they are 
not so distinct. This is especially in- 
teresting when we study the fossils of 
trees which in many cases show a 
great difference in climatic conditions 
in the early ages from those we have 
at the present time. 
The layers of bark are much thinner 
than those of the wood and are not so 
readily distinguished. They are formed 
from the interior so that the oldest are 
on the outside. The older ones fall 
off, however, so that we cannot trace 
sap-wood is the softer wood outside | as many rings in the bark as we can in 
54 
