222 | MR. 8. LE M. MOORE’S STUDIES 
formly towards the source of illumination, or “ photometric,” 
inasmuch as light is approached or receded from according to its 
intensity. The phenomena of photolysis would seem to be ex- 
plicable on the view that this phototactic quality of zoospores is 
a general property of cell-protoplasm. But besides zoospores, 
the Myxomycete plasmodium has been shown by Baranetzky * 
modifiable by light, since the pseudopodia, emitted on all sides 
in darkness and low light, are, when strongly illuminated, drawn 
in upon the more highly lighted, and developed upon the shaded 
side. 
The doctrine advanced here is, that the movements of chloro- 
phyll have no relation whatever to benefit or injury experienced 
by the grains, nor necessarily to the well-being of the protoplasm, 
but that just as in Strasburger’s “ Lichtstimmung " experiments, 
in which a zoospore moved towards or away from a certain degree 
of illumination, according as to whether it was of low or high 
grade, so in respect of any plant there are two points in the 
photrum—the positive and negative critical points—at one of 
which its protoplasm begins to be repelled from the superficial 
to the side wall, and at the other to be turned in the reverse 
direction; in short, it is submitted that all the phenomena are 
to be explained on the supposition that protoplasm is phototactic 
—negatively to light of high, and positively to light of medium 
intensity.. 
Before proceeding to dwell upon this theory in detail, it will 
be well to refer to another matter closely connected with it. 
Suppose that a Funaria-leaf, removed from darkness in which it 
has lain overnight, be set in good diffused light: the protoplasm 
tends to collect upon the surface-walls, and, in so doing, a strain 
is imposed upon its micelle. If the leaf be now brought up into 
sunlight, an increased strain is experienced by the protoplasm as it 
makes for the side wall. Now the elastic recovery of solid bodies 
submitted to twists or strains depends upon, first, the amount, and, 
secondly, the duration of the disturbance; and I shall endeavour 
to show that the movements of protoplasm can best be explained 
on the supposition that it is affected by light just as a solid body 
is by a twist or strain. One of the most remarkable facts about the 
changes of position shown by chlorophyll is that negative apo- 
strophe is so slow in establishing itself in the aquatic plant, while 
it is rapidly induced in ordinary aerophytes. It will be remem- 
* Mém. Soc. Hist. Nat. de Cherbourg, xix. 
