68 CONFERVACE^. 



filaments are enclosed within a common gelatinous envelope, and thus formed into 

 somewhat compound fronds. In the great bulk of the Order no fructification other than 

 minute zoospores has been observed. These are formed out of the colouring matter of 

 the cells, are furnished with vibratile cilia, and when they escape from the cell in which 

 they have been organised, enjoy for a time active powers of locomotion. At length fixing 

 themselves to some object they change their form, becoming cylindrical ; and then, 

 dividing repeatedly, are changed into articulated filaments similar to those of the parent 

 plant. In the Confervm the frond lengthens in two ways ; either by the repeated 

 bisection of all the cells of the frond, as is usually the case in the unbranched species ; 

 or by the evolution of new cells, constantly at the apex of the terminal cell, as is com- 

 mon in the branching species. In these latter the cell, after having once formed one 

 or more new cells out of its apex by a cutting off of the summit from the basal portion, 

 remains unchanged, without further growth or- cell division. If but one new cell be 

 formed at the apex, the filament will be simple ; but in the branched species two or 

 more cells are formed, the central one continuing the frond, while the lateral ones, which 

 spring just below the summit of the old cell, grow out into branches. 



The Confervacese are almost universally dispersed in water of every character 

 found on the surface of the globe. Many are marine, but perhaps the largest number, 

 at least of individuals, if not of species, are found in fresh water. The marine species 

 usually grow within tidal limits, but several of the Cladophora? occur in the Laminarian 

 zone, and some even at a greater depth. The fresh water species are found in lakes 

 and ponds, in rivers, streams, and wells, and in thermal springs or in mineral waters. 

 A large number of genera and species have been described ; but I fear the proper 

 number of both genera and species has been much exaggerated, and that multitudes 

 must be erased from the list whenever the Order shall be carefully revised. The fresh 

 water species have as yet scarcely been attended to in America. I have received very 

 few of these, and most of them in a state unfit for examination. Indeed, dried specimens 

 of such obscure algae are of little value for determining species. A few of the more 

 remarkable are here described ; being all those that I can clearly make out from the 

 specimens received. It is, however, often a difiicult task either to refer one of these 

 species to its supposed type, or to devise specific characters that shall not be illusory 

 for what appear to be new forms. The characters usually msisted on, namely, the 

 length of the cells as compared with their diameter, the absolute diameter of the cell, 

 and the degree of ramification of the filament, are all subject to much variation. There 

 appear to be no definite limits to any of these characters in any species. We are 

 forced therefore, in describing them, to be content with rude approximations. Figures 

 are of little use, for in many of the species, such as Chadophora glomerata, scarcely two 

 specimens are in all respects similar. 



