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OF THE STIPITATE DIATOMACEA2. 
CHAPTER IV. 
OF THE STIPITATE DIATOMACEA2. 
The fact that certain kinds of Diatomaceae are attached 
to other bodies by a footstalk or pedicel, not 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.(I?hrenberg), Sphenella ( Kictzing ), and Gompho- 
nema ( Auct .), Achnanthidium (. Kutzing ), 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 is 
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 ), Rhrpidophora ( Ehrenberg ), and 
Licmophora ( Agardh ), 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 Diatomacese 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 Algae 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, 
