IN VEGETABLE BIOLOGY. 249 
80 far as this evidence goes, there is reason to support the con- 
tention that increase in the intensity of illumination does 
markedly quicken the speed of the rotating stream. 
On Negative Rotation. 
One objection may be taken to the parallel drawn between 
photolysis and rotation. It might be urged, with justice, that if 
this parallel is a true one, it ought to exhibit itself under 
darkling conditions as well as in light. The chlorophyll of 
Elodea or Vallisneria, for instance, ought then, after apostro- 
phizing in the dark—provided, of course, that death have not 
ensued—to commence rotating round the cell; so that just as 
high illumination and darkness are both inducers of apostrophe, 
80 rotation should be the result either of an increase in the 
intensity of light or of its complete absence. I have not as yet 
been able to pursue this interesting subject far; but the facts 
Which follow show that a form of rotation, which may be called 
“negative” in distinction from ordinary or “ positive” rotation, 
—which, however, it precisely resembles—ensues upon prolonged 
Withdrawal of light*. Moreover this might have been pre- 
dicated from the massing in its cells' corners or arms which chlo- 
rophyll experiences when deprived of light, since it has been shown 
that such massing is a mechanical consequence of slow movement 
of the grains round the side-walls of the cell—in other words, of 
feeble rotation. 
In both the external and the internal cells of Vallisneria-leaves 
after three months’ darkness, rotation may be observed, not 
indeed throughout the leaf, but at a short distance from its dying 
apex. At the apex the cells are plainly dead, the protoplasm is 
quite motionless, and the small brown degraded chlorophyll 
grains are for the most part collected in little masses at various 
points. Below this comes a zone where the protoplasm carrying 
the small chlorophyll grains is in slower or quicker rotation. We 
have already seen that protoplasmic movement is more readily 
set up in the large internal than in the external cells ; this 
* Frank noticed that the protoplasm of Zlodea plants kept several weeks 
in darkness, and whose chlorophyll was in [negative] apostrophe, had passed 
into circulation ; but no grains were carried along by the streaming protoplasm. 
Thus he nearly discovered negative rotation ; and would undoubtedly have done 
0 had his experiments continued a few days longer. 
