30 OF THE STIPITATE DIATOMACEiE. 



CHAPTER IV. 



OF THE STIPITATE DIATOMACEiE. 



The fact that certain kinds of DiatomaceaB are attached 

 to other bodies by a footstalk or pedicel, no't only forms a 

 convenient ground of division to the collector, but has a 

 specific value in the eyes of the systematise That this is 

 so is proved by such genera as Cymbella (Agardh), and 

 Cocconema (Ehr enbe rg), Sphenella (Kutzing), and Gompho- 

 nema (Auct.), Achnanthidium {Kiltzing), and Achnanthes , 

 (Bory\ which are respectively separated solely on this ac- 

 count. Cymbella and Cocconema, for instance, are precisely 

 the same in form and appearance, except that the former ig 

 free and the latter stipitate. So with regard to many 

 species of Synedra, great attention is paid to the manner in 

 which they are attached, some being adherent during the 

 whole term of their existence, while others become free at 

 a very early stage. And a single glance at the genera 

 Podosphenia {Ehrenberg), Rhipidophora {Elirenberg), and 

 Licmophora (Agardli), is sufficient to show how much of 

 the characteristic differences existing among these plants is 

 made to depend upon the existence and position of the 

 footstalk. 



The stipitate Diatomaceag must naturally be searched for 

 in somewhat different localities to those in which the free 

 species love to dwell. They are, in fact, to be found ad- 

 hering to the larger Algse and similar water plants, often in 

 enormous quantities. If the smallest atom of one of these 

 loaded plants is separated from the parent branch, and 

 carefully spread out, with the aid of a needle, on a glass 

 slide, then allowed to dry, and submitted to the microscope, 



