242 MR. S. LE M. MOORE 8 STUDIES 
and at 2.20 p.M., on removing the two sections from darkness, no 
rotation at all was observed in one portion, and in the other only 
in the immediate neighbourhood of a diseoloured spot near the 
margin, but far away from the section-edge, and in one cell near 
the base close to a purple discoloration of the cell-sap*. That 
sectioning had lowered the protoplasmic tone was evident from 
the fact that the chlorophyll in the cells upon the section-edge 
was for the most part in apostrophe, epistrophe of course pre- 
vailing elsewhere. 
Moreover, rotation at the section-edge can be stopped by 
withholding light. In a piece of leaf with rotation in the edge- 
cells set over-night in darkness, quiescence may be established on 
the following morning, but frequently a longer time is required. 
This is only what would be expected; for the condition of 
equilibrium between the tonicity of protoplasm and the 
eyclolytic action of light which has been upset by sectioning 
would tend to be restored when the direct access of light is 
prevented. 
With respect to Vallisneria, Ihave not found that sectioning 
is not necessarily followed by rotation in the large inner cells of 
the leaf, even if the utmost care be taken to protect the leaf from 
undue illumination during sectioning. There are two causes for 
this failure: one is that the Vallisneria-plants obtained of the 
dealers, growing as they do under artificial conditions, cannot be 
in a very robust condition ; the other seems to reside in the form 
of the cell and in the relatively small size of the chlorophyll 
grains—both circumstances favourable to rotation, as has already 
been mentioned. This question can be decided only by an appeal 
to healthy plants growing in their native haunts. 
But whatever. doubts Vallisneria may cause as to the error in 
Frank's doctrine, that error is plainly manifested when the proto- 
plasm of intact organs is set in rotation. In view of the ease 
with which this can be done, it is astonishing that incorrect 
notions should have prevailed so long upon the subject t. More- 
over, rotation without injury is similar in every respect to that 
which follows upon sectioning, as the following experiment, 
* It should not be forgotten that the leaves must be cut in very low light: 
in the above and similar experiments the room was darkened by drawing down 
and shutting close a venetian blind at the only window. 
f Frank describes rotation in old and apparently intact leaves af Elodea. 
See also footnote on p. 240, 
