2 
CHLOROSPERMEtE. 
The Chlorosperms are decidedly the lowest or simplest in structure not only of the 
Algae, but of all plants. A very considerable number of them have the frond composed 
of a single utricle or cell, and all cell-division in such plants issues in the production of 
new unicellular fronds. The Orders Diatomacece and Desmidiacece , of which some 
hundreds of genera, and perhaps thousands of species are now known to Botanists, are of 
this character. In the whole of these, the frond consists of what may be called a bivalve 
cell ; the primordial utricle being single while the cellular envelope is divided 'into two 
halves by a medial line. When such a cell is about to be multiplied by dividing into 
two, the two halves of the old cell remain unchanged, and a new growth of two new 
half-cells originates at each side, along the medial line. While this growth is going on, 
the old half-cells are gently pushed asunder, and when it is completed, a separation takes 
place, and two new fronds float apart, each of them composed of an old half-cell and a 
new growth which gradually acquires all the characters of the opposing valve. But the 
unicellular structure is not confined to such minute atoms as the Diatomacese, or such 
imperfect organisms as the Protococcus and its allies. Many of the larger Chlorosperms 
are essentially unicellular, and in some of these the vegetable cell is found of very much 
larger size than in any other plants. In Codium , Vaucheria , and Bryopsis single 
cylindrical cells may be obtained several inches in length, and frequently of consider- 
able diameter. In Valonia , saccate cells sometimes as large as a walnut and often as large 
as a hazel nut, are found. Botrydium , a little siphonaceous Alga common on damp 
ground in Europe, exhibits within the compass of a single branching cell all the ordinary 
organs of a compound vegetable, as much specialized as is possible within such narrow 
limits : thus, it has a descending axis or root, an ascending axis or stem, and a vesicular 
body, within which its spores are developed. In Caulerpa , however, if the frond in that 
genus be really constructed by the evolution of a single cell, we have the vegetable cell 
assuming its highest development and attaining gigantic size. These unicellular (?) 
fronds are sometimes two feet in length, and excessively branched ; with specialized 
root, stem, branches, and leaves. 
The ordinary fructification of the Chlorospermese consists of zoospores , or spores 
endowed with ciliary motion, which have already been spoken of in the General Intro- 
duction, (Part I. pp. 13-14). These are usually of very minute size, and are formed 
within the cells of the frond, by the transmutations of the whole cell-contents. Myriads 
of moving granules are thus evolved, each of which is pointed at one end, and there 
furnished with two or four vibratile hairs, which act like oars, and drive the granule 
through the water. In one instance (Hydrodictyon) the zoospores, whilst still 
retained within the walls of the mother, cell, arrange themselves into a young frond, 
which issues from the cell perfect in all its parts. But usually they are dispersed in the 
water, and swim about until they commence germination. In some cases, a solitary 
zoospore and that of large size, clothed all over its surface with cilia, is formed from 
the mass of endochrome of the parent-cell. And often, as in Zygnema and its allies, the 
spore is the result of the union of the matter of two cells. 
Among the more interesting observations recently made on the development of these 
Algae, Pringsheim’s memoirs on the fertilization of their spores by means of spermato- 
zoids are specially worthy of notice. Male organs of unquestionable character have 
