In Cerámium rúbrum, which is also very common, being found attached to stones, rocks, and the larger Algæ, the filaments ([Pl. IV.] fig. 12) are stouter than in C. nodosum, branched so as to form tufts from 2 to 10 inches long, and their ends forked, with the tips hooked inwards (fig. 14). The central cells of the filaments are large and rounded, and their walls are entirely covered with a layer of very small angular red cells. The globular capsules (fig. 15), or favellæ, are situated on the suter surface of the branches, stalked, and supported by 3 or 4 short branchlets. The tetraspores (fig. 13) are imbedded in the branches, towards the ends. The capsules called favellæ differ from the coccidia in the walls being simply membranous, while the walls of the coccidia, like those of the ceramidia, are composed of cells.

The tetraspores are usually imbedded, among the cells of the superficial layer of the filaments, and are not very easily recognized by an unpractised eye; it will be observed in the figures that they are sometimes cleft horizontally, at others obliquely.

Confervoid´eæ.—This Order consists principally of the green freshwater Algæ, although some of them are yellowish brown, purple, or red, and some are marine. Their general structure may be best illustrated by selecting certain common examples from the families composing the order. The families are 13 in number. The species which are figured in the plates are found in fresh water, except when otherwise stated.

PLATE V. [[PAGE 70.]]
Freshwater Algæ.
Fig.
1.Conferva floccosa, single filament.
2.Lyngbya muralis, single filament.
3.Ulothrix mucosa (?), filament.
4.Synedra radians, prepared frustules.
5.Synedra radians, tuft of natural frustules.
6.Cladophora crispata, with zoospores (a).
7.Batrachospermum moniliforme, portion of filament.
8.Batrachospermum moniliforme, filament.
9.Closterium acerosum.
10.Draparnaldia glomerata.
11.Spirogyra quinina.
12.Spirogyra nitida, filaments conjugating.
13.Zygnema cruciata.
14.Coleochæte scutata.
15.Xanthidia in flint.
16.Micrasterias rotata.
17.Gomphonema acuminatum.
18.Gomphonema acuminatum, prepared frustules.
19.Ankistrodesmus falcatus.
20.Pediastrum Boryanum.
21.Hyalotheca dissiliens.
22.Pinnularia viridis.
23.Fragilaria capucina.
24.Fragilaria capucina, prepared frustules; s* side view of F. virescens.
25.Scenedesmus quadricauda.
26.Schizogonium, probably a form of Lyngbya.
27.Campylodiscus costatus.
28.Nitzschia minutissima, front view.
29.Nitzschia minutissima, valves.
30.Epithemia turgida.
31.Diatoma elongatum, natural frustules.
32.Diatoma elongatum, prepared frustules.
33.Cocconeis placentula.