Chap. III.] DOWNWARD GROWTH OF THE ROOT. 
113 
is caused by it. But, on the contrary, as 
vegetable growth is in opposition to gravity, so 
I think it is caused by one of the great anta¬ 
gonist powers to the attraction of gravity and 
cohesion, — namely, turgescence, or expansion. 
This beautiful experiment, however, relates 
only to the vertical growth of plants upward and 
downward; and has no reference whatever to 
the growth of either head or root horizontally, 
or at any angle with the horizontal line, either 
upward or downward. Indeed, if the experi¬ 
ment proves any thing, it proves that all vege¬ 
table growth must be vertical, either upward or 
downward. The experiment, too, is made on 
the tap-root and first gemmule of the seedling, 
the cellular structure of which I believe in each 
case to differ from that of all other parts of 
plants. 
But looking on the experiment simply as re¬ 
garding the vertical growth of the tap-root and 
gemmule of the seedling, or of any vertical 
growth of a plant, if we are to believe that this 
vertical growth is caused by gravity, it would be 
a case of credo quia impossible. For to say 
that the sap or the new shoot—that either of 
these, the heavier, should be caused to ascend 
through the air, the lighter, by its weight, is as 
I 
