116 BOTANICAL GAZETTE [ AUGUSI 
That the outer layer of cells is not, in this case at least, exclusively 
instrumental in effecting torsion, was proved by scraping off the outtr 
two thirds of a wet awn, when the remaining central portion, on dry: 
ing, was seen to twist as perfectly as the intact awn. Another evident 
of this fact is, that after maceration, the largest cells, which belong 10 
the middle portion of the awn, are found twisted quite ‘as much as tht 
smaller outside cells (fig. g). This also agrees with Darwin’s obser 
tions, quoted by Zimmermann (/. ¢., p. 551). | 
There can be no doubt, then, that the mechanism is in the ind: 
vidual cells, and in the inner as well as the outer; and we have as # 
of cellulose-like material, the molecular structure of which is spiral. 
There are two causes present, either of which may under favorable © 
circumstances produce torsion: 
First, the mechanical cell may be considered as a hollow cylindet 
whose walls are made up of material in layers of alternating densi)” 
In the diagram (fg. 5) let fe and hg represent dense layers of matt 
rial while the less dense are the layers between. When dry, the cells 
twisted with watch hands. Water enters first into the less dense /#} 
ers forcing the micelle in all directions. ‘Two of these forces 
principally concerned here. The one, aé, acting at right angles © 
the spiral plane of more dense material, may be resolved into its es 
components ax and xd. One of these acts tangentially and wth 
simply to increase the diameter of the cell; the other moves the ee 
plane in such a way as to increase the angle it makes with the a8” 
the cell, producing, in the wall of the cell toward us, motion ai 
right to left. The other force, ac, may be resolved into its ee 
nents, ay and cy, the first of which again merely tends to increase i 
diameter of the cell, and the second, acting nearly parallel to the & - 
ponent ax, will strengthen it. In the opposite wall of the cell ® 
same forces will be found to produce the same result, but when o 
through the cell, the direction of motion will be just opposite + : 
in the wall on this side. There can be but one result from the : 
of such forces — the two forces on opposite sides of a cell, acting ” : 
Opposite directions about its center, will produce torsion. spot ) 
Second, the eccentric position of the cellulose-like material | < 
the lumen of the cell throws the center of the more dense materi 
one side of its axis, so that the dry cell on imbibing watet will 
