OF THE CHARACTERISTICS OF THE DIATOMACEA2. 41 
himself, especially in the early spring, when the process of 
multiplication is being rapidly carried on. Melosira va- 
rians, Odontidium, 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 
4 sides ’ are the silicious membranes j?-g 
which, from their enclosing the contents d 
of the plant, are more appropriately 
named 4 valves,’ while the 1 front ’ is the 
frame or hoop, as it is generally termed, 
which binds the flinty surfaces together. 
It is on the valves (that is to say, under 
I a 1 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 Diatomacem 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 
