AN EVENING AT THE MICROSCOPE. 183 



What gives to the plant this power of independent 

 movement ? Does it possess tiny hairs, or cilia, with 

 which it lashes the water or rows itself along, or is 

 the cause to be found in the generation and ex- 

 halation of oxygen ? Here is a question which I 

 have to confess I am unable to answer, although 

 I have peered at these fairy-like organisms with 

 prolonged and tireless curiosity through almost the 

 best optical apparatus that science can supply, and 

 I could wish my readers no better fortune than that 

 they might hit upon this well-guarded secret of 

 Nature. For those who possess good appliances I 

 would suggest this problem for their study. The 

 desmid should be carefully observed on a dark 

 background, with and without a condenser, in a 

 natural condition, and also stained with aniline dyes. 

 But these are details into which I have promised 

 not to enter now. 



It is not difficult to cultivate desmids. They 

 should be kept in a watch-glass filled with their own 

 native water, and covered over with a plate of glass 

 to keep out dust and prevent too rapid evaporation. 

 If absolutely necessary to renew the water, a little 

 rain-water should be added. There are two methods 

 by which desmids reproduce themselves. The first 

 is by cell-division or fission. The clear space in the 

 centre of the desmid may be seen gradually en- 

 larging, without, however, the fracture of the 

 membrane. In the course of two or three hours 

 the two halves are separated, each commencing to 

 grow and continuing till the parent form is reached. 

 Another method of production is that called con- 



