1.] MICROSCOPIC PLANTS. 9 
‘sion. Fig. 8 is a lovely form called Clostertum, found 
in myriads at the bottom of ponds. In both these 
Fic. 7. Fie. 8. 
species the plant consists of two cells. In fig. 9 
(Pediastrum) there are a large number of cells united 
into a spherical form, each cell having two processes 
from it which give the compound plant a stellate 
appearance. In Scenedesmus (fig. 10) the cells are 
united side by side, and the two extreme cells of the 
series are provided with long filaments. These all 
belong to the order of Desmids. They are totally 
distinct from the Diatoms—which we shall allude 
to presently—but in several points they somewhat 
resemble them. Multiplication takes place by divi- 
sion, though in a somewhat peculiar manner. Thus 
fic. 7 shows Cosmarium dividing ; the two outer cells 
formed the old plant, and the inner ones are those 
newly formed. The next change to take place would 
be a division between the two new cells, and thus 
two separate plants would be formed, each consisting 
of a new and an old cell. The same process goes on 
in the other Desmids. The Dzatoms (figs. 11, 12, 13) 
are all encased in little boxes, composed of pure 
flint formed into two valves, one of which fits into 
the other, just as a pill-box fits into the lid. They 
are not green like the Desmids, but yellow-brown. 
Like Volvox, the Desmids, and other plants, the 
Diatoms have been claimed as members of the 
