224 MR. 8. LE M. MOORE’S STUDIES 
has been placed in darkness, there is set up in the protoplasm of 
its cells a tendency which, if unchecked, would cause accumula- 
tion of the protoplasm on the superficial walls, and consequent 
epistrophization of the chlorophyll. What are the forces con- 
ditioning the setting-in of this movement? Plainly, the mo- 
mentum of the protoplasm diminished by the inertia of the grains ; 
the retardation due to friction of, first the protoplasm against 
the wall, secondly the grains against the wall, thirdly the 
protoplasmic stream against the grains; and, lastly, the loss of 
momentum consequent upon impact of the grains upon their 
fellows. If, therefore, there come into play another force equal 
to the difference between the momentum capable of being accu- 
mulated in the protoplasm and the retarding forces, and acting 
in the same way as the latter, no epistrophization can take place. 
In the Funaria-leaf under notice this force is none other than 
the force by which negative apostrophe is brought about, and 
the considerations just cited account for the fact that, although 
the latter force comes more tardily into play than the epistro- 
phizing force, the positively apostrophized grains of darkling 
Funaria-leaves do not pass into epistrophe. But in the cell of 
a darkling aquatic plant, with positively apostrophized ehloro- 
phyll, a very different state of things exists. Here light has im- 
posed a greater strain upon the protoplasmic micell®, and re- 
covery should be more gradual. The first portion of the strain 
to begin to disappear will obviously be that by which positive 
apostrophization was caused: this would be the signal for epis- 
trophization to commence and finally to prevail, it not having 
been checked or prevented by an opposing negatively apostro- 
phizing force, because, as is shown by the table on p. 234, nega- 
tive apostrophe, on account of the slow rate at which effects 
produced by light soak out of aquatic protoplasm, does not set 
in until some weeks after light has been withdrawn from aquatic 
types. 
If the present argument be sound, the time taken by proto- 
plasm to recover from the effects of insolation should vary di- 
rectly as the time of exposure. It may be stated as a general 
rule that this is undoubtedly the case. The easiest way of ap- 
plying this time test is to experiment with plants whose grains 
have been driven, some into simple, some into massed apostrophe, 
epistrophization from the latter phase requiring much longer 
than from the former. I believe the statement is also true of 
