In Gónium pectorále (fig. 11 a) the green bodies, which are sixteen in number, and furnished each with two cilia, are grouped into a flat square plate; and in the very minute Gonium tranquil´lum (fig. 11 c) these bodies are also sixteen in number, and arranged in a tabular form, but are without cilia.

Siphona´ceæ.—The structure of this family may be illustrated by the genus Vauchéria, of which two or three species are common on damp ground or in freshwater pools, forming a green layer. At first sight, the filaments of which the little plants consist appear like those of a stout Conferva; but on close examination they are found to be branched, and not jointed, consisting of a single cell from end to end ([Pl. VI.] fig. 26). The reproduction is effected by the agency of two kinds of organs, antheridia and capsules (sporangia), situated near each other (fig. 26 a) on the walls of the filaments, of which they are protrusions or outgrowths—their cavities being separated from that of the filament by a partition or septum. The antheridia produce spermatozoa, and the sporangia each a spore, the one fertilizing the other in the ordinary manner. In addition to this method of fructification, zoospores are also produced—the ends of the filaments becoming swollen, the contents cut off by a septum, and forming single large zoospores covered with cilia, the further development of which resembles that occurring in the Confervaceæ.

Oscillatoria´ceæ.—The members of this family are commonly found in stagnant water or on shaded damp ground, especially in the cold seasons of the year, forming green strata or masses.

TABLE VI. [[PAGE 84.]]
Freshwater Algæ.
Fig.
1.Oscillatoria autumnalis.
2.Oscillatoria nigra.
3.Coscinodiscus radiatus.
4.Nostoc minutissimum.
5.Actinocyclus undulatus.
6.Bacterium.
7.Rhabdonema arcuatum.
8.Rhabdonema arcuatum, prepared frustules.
9.Melosira nummuloides.
10.Melosira nummuloides, prepared frustules.
11.a, b, Gonium pectorale: 11 c. Gonium tranquillum.
12.Spirulina oscillarioides.
13.Synura volvox.
14.Synura volvox.
15.Gyrosigma attenuatum, front view.
16.Gyrosigma attenuatum, side view; 16 a, portion of a valve.
17.Gyrosigma angulatum; 17 a, portion of a valve.
18.Volvox globator.
19.Glœocapsa.
20.Chara vulgaris, globule.
21.Chara vulgaris, portion of filament.
22.Chara vulgaris, branch with nucule and globule.
23.Tabellaria flocculosa.
24.Tabellaria flocculosa, prepared frustules.
25.Palmella cruenta.
26.Vaucheria Ungeri (sessilis).
27.Vaucheria Ungeri, capsule.