THE STEM AND THE BRANCHES 
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secrets jealously; they have had to work through dis¬ 
couragement that would have made you or me give up 
long ago, and there are still many secrets which Nature 
has not yet yielded to their understanding. And this is 
one of them: 
What makes the sap run up the tree ? 
We said a while ago that the tree stem has two duties 
to perform; it holds the branches aloft, spreading the 
leaves to the sun, and it serves as a channel through which 
water containing plant food—in other words, the sap— 
rises and flows from root to leaf and down again to 
nourish each living part. But what makes the sap rise? 
There is no giant lying hidden in the earth, ready to put 
his mouth to the stem base and puff out his great cheeks 
and blow the sap up the tall trunk to the highest twig! 
And there is no wood fairy on the highest leaf to put her 
lips to the twig and with a magic breath suck the sap up 
from the roots! Boys and girls, what makes the sap 
circulate in your own healthy bodies ? Blood, you know, 
is our sap; it flows from our toes to our finger tips to 
nourish the living cells of our bodies. And what makes 
it flow? The heart, you say! And right you are; the 
heart is the strong and tireless engine which pumps the 
blood through our limbs. But who can find the heart of 
a tree, or who can discover any strong pump to send the 
sap spurting up the trunk ? 
