OF THE DESMIDIACEAS AND SIMILAR MINUTE ALGAS. 53 
account with that from a spring, as its ‘ hard ’ property is 
sure to kill the plants. Care must be taken also not to ex- 
pose the vessel to too much heat ; in fact, it had better be 
set in the shady part of a window, where it is screened from 
the direct rays of the sun. 
The student must not expect too much from this method 
■of multiplying the Desmids. It does well for a while; 
but there is no doubt that, in the course of time, the 
plants degenerate, and cease to be fair representatives of 
the species. 
[The figures (61 to 70) on Plate xm. will give the young 
student an idea of the manner in which the Desmids 
propagate themselves. They are examples of the common 
constricted species, Cosmarium botrytis. 
In figs. 61 to 64 we see how the two portions of the 
frustule gradually separate themselves, new cells forming 
in the interior, which ultimately become perfect frustules. 
This mode of propagation is known as ‘ cell division.’ By 
another method, called 1 conjugation ’ (of which more will 
be said hereafter), two frustules, which chance to lie near 
each other, form a temporary union, and mingle their 
contents together, figs. 66 to 69. The mass takes an 
irregular form at first, but gradually assumes the shape 
.given in fig. 70, viz. a globe covered with forked processes 
(a, b). This globe, or sporangium, as it is named, gives 
birth to new plants — -Ed.] 
Where the observer is content to study the external 
form only, the plan of simply drying his specimens on a slip 
of glass is sufficient ; because, on re-moistening them, the 
plants resume their former appearance. If, on the other 
hand, he wishes to examine the peculiar arrangement of the 
Chlorophyll), and the other contents of the cell, after the 
object has been laid by, he must preserve them in some 
fluid which will not alter their natural form and structure. 
Much time also is saved by his having such preparations 
ready to hand for comparison and observation. Moreover, 
.many of the smaller Confervas (such as Zygnema and 
