212 FIRST FORMS OF VEGETATION. 
mica, which effectually excluded the outer air, and 
kept the water as motionless and fixed as a piece 
of ice. The glass, with its contents thus arranged, 
was placed under the microscope, and the oscilla- 
tion of the filaments was observed most vividly, 
there being no possibility of disturbance by the 
agitation of the water, showing clearly that the 
singular movement was independent of that cause. 
‘The action of light,’ says this accomplished natur- 
alist, ‘as a cause of motion, cannot be directly dis- 
proved, because we cannot view our specimens in 
the dark; but indirectly there is nothing easier. 
If a watch-glass, charged as above, be laid aside 
for a night, it will be found that by next morning 
not only a considerable radiation has taken place, 
but that multitudes of the filaments have entirely 
escaped from the stratum, both indicating motion 
independent of light. Rapidity of growth will 
show itself in a prolongation of the filaments, but 
will not account for this oscillation to the right 
and left, and still less for their travelling in the 
course of a few hours to the distance of ten times 
their own length from the stratum. This last is a 
kind of motion unexampled, I believe, in the vege- 
table kingdom.” Many species, it may be re- 
marked, possess at their extremity a tuft of very 
minute, delicate cilia, which possess the power of 
imparting motion to the filaments on which they 
