the wood, although one is formed in | 
each for every season that the tree 
lives. 
The roots of the tree spread out un- 
derground and are the agents through 
which the tree derives most of the 
moisture so necessary to its growth. 
They absorb moisture only at their 
extremities and usually spread to just | 
such an extent that the water which 
falls off the outer branches of a tree | 
during a rain, falls exactly where the 
tender rootlets can gather it up at 
once and hurry it back up the trunk 
of the tree. In ground that is springy, 
or naturally moist, the roots do not 
depend so much on the rainfall but 
reach out after moisture wherever it 
exists in the soil. 
Spring seems to give a new impulse 
to life, especially to vegetable life, 
which always responds promptly to the 
genial rays of the sun. During the 
winter, in our climate, the cells which 
form our trees are contracted by the 
cold and when the warm days cause 
them to resume their natural size, a 
small vacuum is formed in each cell, 
which the first warm days proceed to 
enlarge by thawing only the trunk and 
branches of the tree, leaving the roots 
below embedded in frozen soil from 
which but little moisture can be drawn, 
while evaporation draws moisture from 
the trunk and branches with irresistible 
force. A warm rain now comes, thaws 
out the soil, and sets the juices therein 
contained in motion. An immediate 
rush of sap up the trunk of the tree is 
the result. It clears out the pores or 
channels, as a spring freshet clears 
out the water courses, it rushes into 
the branches, and the branches re- 
joice) sand put: on itheire livery. of 
green; it rushes out through the por- 
ous surface of the limbs and rises in 
the air in the form of vapor, while that 
which does not escape becomes charged 
with life and returns down a devious 
pathway and lays the foundation for 
another season’s growth. 
But why should the sap ascend the 
Eneer 
This is only one of many questions 
that the tree will not answer and no 
one else ever hasanswered. If wetake 
a strip of blotting-paper and insert one 
55 
end of it in an ink-well, the ink imme- 
diately begins to climb up the blotting- 
paper by means of the force known as 
capillary attraction. Here, says the 
seeker for truth, is the reason for the 
ascent of sap, and many profound au- 
thors have agreed that he is right. 
Others claim, however, that he is 
wrong, while still others think he is 
only partly wrong and that this force 
has something to do with it. If we cut 
the roots from a tree and insert the 
stem in water we will soon find that 
this force is not the sole cause for the 
ascent of sap. Another student has 
made experiments with the force called 
diffusion, and claims that this explains 
the rise of sap to such remarkable 
heights; but diffusion does not work 
fast enough and hence must be thrown 
aside. Another finds that water is im- 
bibed through fine porous substances 
with great force and that air can thus 
be compressed to several atmospheres, 
and this force is affirmed to be the 
one at work in our trees. But the fact 
that the amputation of the leaves and 
branches checks the ascent is brought 
forward and this theory falls to the 
ground. The fact that liquid films 
have a tendency to expand rapidly on 
wetable surfaces was next advanced, 
but the objection to the first theory 
met it at once. 
Another interesting theory is now 
brought forward and has the advantage 
of practical demonstration, that is, an 
artificial model was made through 
which water ascended. It is based on 
the principle that water will pass 
through moist films that air will not 
penetrate, on the fact that evaporation 
takes place under right conditions 
with force enough to cause something 
of a vacuum, and also on the elasticity 
of the cells. 
The model was constructed of glass 
tubes, closed at one end with a piece of 
bladder, and joined together in series 
by means of thick-walled caoutchouc 
tubing; the top which represented a 
leaf was a funnel closed by a bladder. 
This artificial cell chain was filled with 
water, mixed with carbolic acid to 
keep the pores from clogging, and was 
set up with its base immersed. The 
fluid evaporated through the membrane 
