Cytology and Movements oj the Cyanophycee. 315 
for the movements of these organisms. Pfitzer (63) has 
raised the objection to it, that the velocity of osmotic cur- 
rents would be so slow as not to cause motion. This is cer- 
tainly a valid objection, notwithstanding the explanation of 
Kozlowski (43) that “the cause of movement does not lie 
in the velocity of the current, but exclusively in the change 
in position at the centre of inertia, and is equally true 
whether liquid flows out through macroscopical or molecular 
openings.” Hansgirg’s efforts (35) to show such currents 
were made by placing Oscillaria filaments in almond oil. 
In this way he found that there was a delicate pellicle of 
water surrounding the organism which was sufficient in 
some cases to cause motion for four days, when the layer 
of water would finally be broken up and the movements 
cease. Such an experiment, it would seem, would be a 
stronger argument against osmotic currents than for them, 
notwithstanding the efforts of the supporters of this theory 
to make out that the movements are very slight, even if they 
look very great on account of the magnification used. When 
we magnify the movements we also magnify the organism, 
and the relation between the two remains the same. Thus 
how the very thin pellicle of water which remains surround- 
ing the trichomes when placed in the almond oil, can be 
sufficient to set up osmotic currents of such magnitude as to 
cause motion, either oscillating or creeping, of several times 
the diameter of the plant, is difficult to understand, as is 
likewise how the delicate, hydroscopic pellicle on the trich- 
omes of the Oscillariee growing on moist soil can cause 
movements over the surface of the supporting substratum as 
claimed by this author, for the delicate film of water sur- 
rounding them as they creep is many times thinner than the 
diameter of the trichome, though the motion passes through 
many times that distance. 
The ingenious ideas of Wolle and some others con- 
cerning these movements being caused by the multiplication 
of cells, are also similar theorizings without any basis in 
