OF THE DIATOMACEA2. 
13 
speaking, the cleanest specimens, by which I mean those 
best adapted for immediate preparation, are the filamentous 
genera of Melosira, Odontidium, Fragillaria, and Schizo- 
nema ; also certain parasitical kinds, such as Cocconeis, 
Achnanthes, Synedra, Gomphonema, Licmophora, &c., 
which often cover the plants to which they are attached 
to such an extent as to hide the original form. 
With regard to the fossil Diatomacege it is a singular 
fact, that although they exist in such countless quantities, 
they are nevertheless ranged under a very small number 
of species. 
As in the case of the Algge generally, the outfit required 
for gathering Diatomacege is of the simplest kind. A 
common iron spoon, to scrape the surface of mud ; a few 
small bottles, wide-necked and cork-stoppered ; a quantity 
of oiled paper, or some similar material. With these few 
articles the botanist may safely commence an expedition 
in search of these minute plants. 
[The collector will often come across likely-looking spots, 
lying beyond the reach of his arm ; perhaps a mass of 
weeds in the middle of a wide ditch, or a tempting hollow 
at the base of a steep slippery bank. To meet this con- 
tingency, he should provide himself with an ounce vial, 
broad-brimmed and wide-mouthed, and, besides, a stout 
india-rubber ring. The bottle, when required, can be 
easily attached to the end of a walking-stick by means of 
the ring (as shown in fig. 24, Plate v.), and then in- 
serted among tufts of Algse, &c., at some distance from the 
side of the pond or stream. — E d.] 
