14 
OF THE FREE DIATOMACEiE. 
CHAPTER III. 
OF THE FREE DIATOMACEJ3. 
The Diatom ace as may be conveniently divided into two 
classes, the free species, or those which have an indepen- 
dent existence ; and the stipitate, or such as are attached to 
other objects, generally the larger A1 gee, by means of a 
stalk. This kind of classification, though purely arbitrary, 
is not without a certain importance, so far as the purposes 
of collection and preparation are concerned ; for, as it is 
one of the main points in a well-ordered herbarium to 
retain the natural habit of each plant, we must not over- 
look the various modes of growth to which the Diato- 
macese are subject. 
[Acting on the Iloratian maxim, that 
* Segnius irritant animos demissa per aures, 
Quam quae sunt oculis subjecta fidelibus/ 
I add here a few examples of the two classes of Diatoms 
referred to above. Figs 25, 26, Plate v., represent members 
of the ‘ Free ’ genera, Navicula and Pinnularia. 
In these it will be seen that each plant is a separate and 
independent individual ; whereas in those* which follow, 
individuals are attached together, or to some other body, 
either by a slender cord, or by a stem, from the ends or 
sides of which they are produced; in other words are 
1 Stipitate : ’ for these see Plates vi. and vii. 
A third form includes the Frondose species, or those in 
which numerous individual frustules are enclosed in, and 
held together by, a coating of gelatine ; bearing, in this 
state, a strong resemblance to the frond of a tiny seaweed. 
Figs 31 to 34 (Plate vm.) belong to this group. — E d.] 
