Transactions Texas Academy of Science. 
93 
at A was artificially produced by bending and tieing, at B by the normal 
geotropic curving. After two or three weeks of this position, the cell 
walls of the entire upper side showed marked thickenings, even those 
at the inner curve A, which, whenever the curve opened in any other 
direction, remained very thin. 
IX. Helleborus niger was subjected to all the experimentation de- 
scribed without in any manner altering the character of the phloem ele- 
ments or the production of new elements, though at all times the usual 
changes occurred in the collenchyma. 
X. In order further to investigate the extent to which tension enters 
into this thickening of tissues, an apparatus which may be called a 
“rocking machine” was employed. This is simply a large clock work 
with a long pendulum, driven by a weight of several hundred pounds. A 
vertical iron rod working upon a bolt through its middle is connected by 
a cross bar to the lower part of the pendulum. The upper end of the 
rod bears a cup for the reception of the flower pot. When the pendulum 
is in motion, the cup and flower pot swing to and fro, the length of the 
arc being readily adjusted by changing the position of the pivot of the 
rod. When now the plant is fastened by means of a thread to a point 
in the plane of the pendulum in such manner that when the plant is 
upright, the thread is tightly stretched, at every second beat of the pen- 
dulum, the plant will be sharply bent out of the vertical. In the mean- 
time the plant rights itself by its own elasticity. If the stem be made 
fast to two points on opposite sides, there results an alternate bending 
from the one side to the other. In this way, the effects of the wind may 
be to some extent reproduced. The tissues on opposite sides are thus 
alternately strongly drawn and compressed. 
At first, seedlings of the plants named were put upon the machine 
without being fastened. These underwent very little bending, even 
when swung through a relatively wide arc. Such plants showed no 
alteration of tissues whatever after having been thus “rocked” for seven 
or eight days. When, however, the stem was fastened, so that a periodical 
bending resulted, there appeared in every case on the outer or stretched 
side, a hypertrophy of the tissues, bast, as well as collenchyma. It must 
be noted, however, that not only is tension at play here, but at every beat 
the plant assumes a more or legs horizontal position, according to the 
length of the arc through which it is swung. During one-half of the 
time, then, it is subject to the influence of gravitation. The cells of the 
side which becomes concave remain thin walled. In many plants there 
appeared the same phellogenlike proliferation of the parenchyma cells 
as already been described. See Fig. 8. Fig. 9 shows a normal. This 
occurred always on the convex side at the point of greatest curvature 
