OF THE CHARACTERISTICS OF THE DIATOMACEiE. 41 



himself, especially in the early spring, when the process of 

 multiplication is being rapidly carried on. Melosira va- 

 rians, Oclontidium, Fragilaria, and numerous other kinds, 

 are invariably produced in this manner, and are to be found 

 almost everywhere. 



It is more difficult to represent the relation which these 

 two aspects bear to each other in species with unequally 

 developed sides, as Cymbella, or in forms similar to those 

 of Biddulphia and Triceratium, Plate x. It may help to 

 guide the young botanist if he keeps in mind, that the 



sides ' are the silicious membranes ^„ 4g 



which, from their enclosing the contents d 

 of the plant, are more appropriately A n\ a 



named c valves,' while the * front' is the jj ! fl 



frame or hoop, as it is generally termed, f ^7 1$ 



which binds the flinty surfaces together. n c I 



It is on the valves (that is to say, under 

 a ' side view ') that we more generally find those wonderful 

 sculpturings which serve the purpose, in a great measure, 

 of distinguishing the species. Perhaps the above remarks 

 will be made clearer by an examination of the annexed 

 fig. 48, in which a, b represent the two opposite surfaces 

 (valves or sides) of a Navicula, and c is the frame (hoop 

 or front) which holds them together. 



In most cases the Diatomaceae offer a valve or side view 

 to the observer, the front or hoop being completely out of 

 sight, or only visible as a narrow line or suture encom- 

 passing the valve. He is therefore compelled, in order to 

 get a full view of the hoop, to change the position of the 

 frustule by turning it round, which is best done while 

 the plant is immersed in water. If it has been already 

 dried, it should first be allowed to remain a short time in 

 alcohol to get rid of the air, which is almost sure to collect, 

 especially in the larger specimens, and mar their beauty. 

 This being effected, let the plants be placed on a stage 

 plate, a drop of water added, and the whole covered with a 



