138 . FOOTNOTES FROM 



straight. They are distinguished by close parallel rings 

 easily separating from each other. The motion of oscil- 

 lation, for which all the species are distinguished, is in 

 some remarkably vivid, and would favour the supposition 

 that they are animals and not plants, were it not that 

 their other characteristics are peculiarly those of vege- 

 tables. The filaments continually move from right to 

 left, or from left to right, but in a very irregular manner, 

 some going in one direction and others in another ; some 

 bei^g at rest while others are in motion. This lateral 

 oscillation has been attributed to various causes. The 

 majority of naturalists, inclining to the opinion that it 

 is mechanical and not voluntary, have ascribed it to 

 rapidity of growth, which, in such simple plants, is ex- 

 cessive ; to the molecular action of light, or to the agita- 

 tion, by hidden causes, of the water in which the fila- 

 ments are immersed for inspection. But none of these 

 suppositions afford a satisfactory explanation, as Captain 

 Carmichael ascertained by the following simple contriv- 

 ance : He placed a small portion of the stratum of a 

 species of Oscillatoria, composed of a great many indivi- 

 duals united together, in a watch-glass filled with water, 

 and covered it with a thin plate of 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 

 oscillation of the filaments was observed most vividly, 

 there being no possibility of disturbance by the agitation 

 of the water, showing clearly that this singular move- 

 ment was independent of that cause. " The action of 

 light," says this accomplished naturalist, " as a cause of 



