34 OF THE STIPITATE DIATOMACEA2. 
In many species (as, for instance, Melosira varians, Odon- 
tidium mesodon, &c.), numerous individuals are united 
together so intimately as to form a sort of chain. These, 
on being detected, may be at once removed from the water, 
laid on paper or glass, and dried. But this must be done 
while the plant is still fresh, for, as soon as its vitality 
ceases, the links of the chain separate, and the whole falls 
into a mass of minute fragments. The connection, however, 
may be preserved for a long time by immersing the plant 
in the alcoholic mixture mentioned above. 
Another manner of growth observed among the Diato- 
macese is that of an amorphous mass of gelatine, or gelatinous 
tubes, enclosing numerous individual plants. Each tube or 
sheath forms a kind of frond, adhering at one extremity to 
the larger Algas, or some similar object under the water. 
Of this kind are Encyonema, Homceocladia, Schizonema, and 
numerous other genera, in which the frond is persistent; 
while in Colletonema and Frustulia the sheath appears to be 
of a more temporary nature ; in fact, to be an abnormal 
development due to the influence of some unknown causes, 
rather than the regular growth of the plant. The beginner 
will be better able to judge of the structure of this group 
of Diatomacese by consulting Plate ix., as also figures 31 
to 34 on Plate vm. 
Finally, in Gomphonella olivacea the stipes, or footstalk, 
appears half dissolved in a kind of mucous matter, in which 
the wedge-shaped frustules are embedded. 
Such of the Algse as have been laid on paper may be 
put away as soon as they are thoroughly dried, without 
any further process but that of attaching a descriptive 
ticket to each, of which more will be said hereafter. 
Those, however, which have been laid on glass, must be 
placed for preservation in a paper envelope. The shape of 
this envelope is of sufficient importance to warrant a figure 
and description, for upon it depends the future safe-keeping 
of the slide. The latter, in fact, must lie so firmly in its 
covering, that the tender plants may not be rubbed off in 
