34 OF THE STIPITATE DIATOMACE^E. 



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 Algse, or some similar object under the water. 

 Of this kind are Ency onema, Homoeocladia, 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 Diatomaceae 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 Algae 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 



