148 ON THE POWER OF MOVEMENT IN PLANTS. 



within, and set free from the A?itheridm of some AI^cb, and also of 

 Characece, Ferns, and other higher Cryptogams ; these resemble 

 the Zoospores in their appearance and motile power, although their 

 mission is of course a different one. 



In both these cases the cilia are the agents of motion, but 

 the internal causes of the movement of the cilia themselves 

 are still among the unknown, let us hope not among the unknow- 

 able. The general opinion, so far, is that the causes are analogous 

 to those of the rotation of protoplasm already referred to. 



D. — Motion of Entire and Adult Plants. 



This is abundantly met with. In many cases — as for instance 

 in the adult Frotococcus, and in the ' cell-families,' such as Volvox 

 globator^ where several unicellular AlgcE unite to form a colony — 

 the motion iseffected by cilia. In others — such as the OscillatoricB^ 

 a filamentous group of AlgcE^ and the Schizomycetes, containing 

 Bacterium^ Vibrio^ Spirillum^ and Leptothrix^ Algae which are just 

 now supposed to be the quite innocent causes of nearly all the 

 diseases to which we can possibly succumb — there are no cilia, and 

 yet their vibratile, oscillating, and creeping movements are perfectly 

 well known, although the causes and mechanics of such move- 

 ments are still involved in obscurity. 



In the Diatoms again, we find brisk activity, and yet no cilia, 

 so far as we know. It is supposed either that they move by minute 

 projections of protoplasm through spots in their shells (something 

 after the fashion of Echinus)^ or that it depends on osmotic 

 currents, due to interchange of matter between their cell-contents 

 and the water in which they live. 



It would be well if a considerable portion of the valuable time 

 and talent devoted to investigating the marking of their shells 

 were spent in working out their life-history, of which next to 

 nothing is known. May be, we should be able to lay part of the 

 odium now showered on the poor unfortunate Schizomycetes^ upon 

 their brethren the Cofijiigatce ! 



CLASS II. 



Movements purely Mechanical and due to Physical 



Causes. 



I say purely Mechanical, because there are many other move- 



