78 OF THE OSCILLATORLE. 



of light, &c.), the operator will observe, even without a 

 lens, a dark filmy mass radiating from the common centre 

 of each piece of water, and spreading equally over the 

 surface. Gradually the edges are reached, and then the 

 filaments bend themselves round, and follow the line of the 

 circumference. To make really good preparations, the 

 greatest pains must be taken not to jolt or shake the paper 

 until the water is entirely dried up, and the Algae lie flat 

 on the spot prepared for them. As soon as this has taken 

 place, the sheet should be removed from the board, and. 

 divided into the several parts marked off by the pencil. 

 Each of the examples is then ready to be deposited in the 

 herbarium. 



The reason why it is advisable to prepare several 

 specimens on a single sheet, and to lax the latter to a board 

 during the operation, is, that the Oscillatorise are of an 

 exceedingly fragile nature, the filaments easily falling to 

 pieces, and the fragments jerking themselves off" the paper, 

 if the latter be crumpled and then suddenly bent straight 

 again, as is sure to happen when it is laid in the her- 

 barium. Now, small pieces of paper do get so crumpled, 

 while they are drying, in consequence of being acted on 

 unequally by the water : whereas large sheets accommodate 

 themselves more readily to the contraction and expansion 

 caused by evaporation ; and consequently the individual 

 sections are smoother and less wrinkled when the whole is 

 cut up. A single experiment will demonstrate this. 



There are certain genera, some of which belong to the 

 Oscillatorian family, the members of which (instead of 

 spreading themselves out like those we have just been 

 speaking of) group themselves into close fiocculent masses. 

 Such are Phormidium, Microcoleus, some species of 

 Symploca, and not a few of the Scytonemacese ; among the 

 Ulotrichaa, Hormidium and Schizogonium ; and of the 

 Zygnemaceas, Zygogonium. In all these forms the filaments 

 have a tendency to develop themselves towards the 

 interior, and their growth is exceedingly complicated in 



