Chap. III.J DOWNWARD GROWTH OF THE ROOT. 
119 
ascend. We are ignorant of where, or how, it is 
elaborated. We are ignorant of the office of the 
leaf. We are ignorant of the office of the pith. 
We are ignorant of what causes the stem to 
grow vertically upward. We are ignorant of 
what causes the branch to grow horizontally, or 
at any angle with the horizon, upward or down¬ 
ward. We are ignorant of what causes the tap¬ 
root to grow vertically downward. And we are 
ignorant of what causes the branch-root to grow 
horizontally, or at any angle with the horizon, 
upward or downward; or of what causes the 
branch-root to grow vertically upward. If the 
vertical upward growth of a root is doubted, I 
can show it now going on to any one who de¬ 
sires to see it. I have myself put the question 
to Nature, and I have her autograph answer to it 
in my possession. In this case of roots growing 
upward, the descensus becomes an ascensus . 
What is called the ascending sap in the wood of 
the root, becomes a descending sap ; and what is 
called the descending sap in the bark of the root, 
becomes an ascending sap.- AYith submission to 
Sir Humphrey Davy, what has gravity to do 
with all this ? 
That this our nineteenth century has infi¬ 
nitely more knowledge of vegetable physiology 
i 4 
