ALGrJS : THEIR STRUCTURE AND MODE OF REPRODUCTION. 27 
tion, and beginning with the lowest, we find the Chlorospore^: 
or ConferyoidEjE to be a heterogeneous assemblage of an 
immense variety of forms, differing most widely from one 
another, and arranged into a considerable number of families, 
whose rank is by no means uniform, and some of which might 
well be raised to the grade of independent orders. We 
propose to describe some only of the more important and in- 
teresting of these. 
Among the lowest forms of this protean order are the two 
families Diatomacece and Desmidiece. The various and ex- 
tremely numerous species belonging to these families are so 
remarkable and peculiar as to have attracted a large share of 
attention, and to have formed almost a study of their own. 
We do not, therefore, propose to enter further into their de- 
scription here. The extreme beauty and fineness of the mark- 
ing of the siliceous coating of the cells of Diatoms have rendered 
them favourite test-objects for the higher powers of micro- 
scopic lenses. The peculiarities of their structure and mode 
of reproduction rendered it long a doubtful point whether they 
belonged to the animal or the vegetable kingdom, the great Ger- 
man authority, Prof. Ehrenberg, having persistently maintained 
their animal character. 
The family of Pal'mellacece or Chroococcacece includes some 
of the simplest possible forms of vegetable life, comprised under 
the designation of Unicellular Algae. In Protococcus the indi- 
vidual consists of a single cell composed of cell-wall and proto- 
plasmic contents (but without a nucleus), the latter of various 
colours. Eeproduction takes place by the ordinary process of 
cell-division, the protoplasmic contents of the cell first becom- 
ing constricted at two opposite points, the constrictions advancing 
till they meet, and thus dividing the protoplasm into two halves, 
the cell-wall afterwards folding in and finally dividing the 
parent-cell into two daughter-cells similar to itself. In this 
instance, however, the daughter-cells which proceed from a 
single parent-cell remain united by a common gelatinous 
envelope. Palmella cruenta forms the well-known rose- 
coloured gelatinous patches found on damp walls, which flake 
off when dry. Protococcus nivalis is the well-known “ Ked- 
Snow,” the wonder of Arctic travellers, a blood-red gelatinous 
substance, which increases with such extraordinary rapidity 
that miles of virgin snow will become covered with it in a 
single night. It is occasionally met with in this country on 
other substances than snow. The family includes also some 
other more complicated structures, as Gloeocapsa and Merismo - 
pcedia . 
In Nostocacece are included some very remarkable forms 
of algae, especially the well-known Nostoc. Emerald-green 
