190 FRESH-WATER ALG^ OP THE UNITED STATES. 



Subfamily CEDOGONIEtE. 



Filamenta stricta, baud ramosa, sine setis veris, sed ssepe apice setiforma, elongata, hyalina. 



Filaments simple, not ramose, without true seta, but often with their apex seta-like, elongate, 

 hyaline. ^ 



Bemarhs. — The CEdogoniacece are small filamentous plants, whose size is sufficient 

 to render them visible to the unaided eye, and yet not sufficient to make each indi- 

 vidual distinctly apparent. They grow mostly in quiet water, attached to almost 

 any and every thing that can aflford a foothold, fringing with apparent indiiference 

 stones, twigs, sticks, dead leaves, bits of glass, boards, etc. I have seen such 

 masses of them crowding the whole surface of a physa as to entirely conceal the 

 animal and its shell, and present the curious spectacle of a perambulating, waving 

 forest of bright green. The individual filament is composed of cylindrical cells, 

 which are always without a nucleus, and have their chlorophyl diffused instead of 

 being collected into bands or stripes. The walls are mostly quite thick and 

 marked near the distal end with circular striae, whose numbers bear relation to 

 the edge of the cell, for these striae are the results of the peculiar method of cell 

 multiplication by division, each one marking one such division. "When an oedo- 

 gonium cell has attained sufficient maturity and is about to divide, the first per- 

 ceptible change is the appearance of a little circular line or streak near its distal 

 end. About the same time and in the same place a fine partition is formed by an 

 outgrowth from the primordial utricle, a probably double delicate wall of con- 

 densed protoplasm separating the upper end of the parent cell from the lower or 

 main portion. The upper end now begins to develop into a new cell. This de- 

 velopment takes place by the formation of an entirely new layer of cellulose 

 inside the little cell, i. e. between the new primordial utricle and the old cell wall, 

 and afterwards by the lengthening of this layer by interstitial deposit in the usual 

 way; the thick wall of the parent cell in no way directly participates in the 

 growth (fig. 2 i, pi. 17). It is evident that as the new wall grows the old cell 

 wall must be as it were raised up upon it, borne away as a little capping from the 

 basal portion of the parent cell. Consequently when a young cell is watched 

 during this process the little line-like incisure of the parent cell is seen to widen 

 until it becomes an evident trench, and this trench grows wider and wider, until 

 at last it is so broad as to be no longer a trench, and the little end of the parent 

 cell simply caps its offspring. When the latter has fulfilled its allotted period oi 

 growth, the process is repeated, the line of separation appearing this time just 

 below the edge of the first cap. It is plain that the second new cell when formed 

 must have a double cap crowning its extremity. At each repetition a new layer 

 is added to. the thickening cap, until at last it may be composed of six distinct 

 layers, each projecting just beyond the next older one. Under the microscope the 

 increased thickening of the distal end of a cell bearing such a crown-piece is not 

 sufficiently evident to at first attract attention, whilst each edge of a layer appears 

 as a stria. It is plain that the number of these striae represents the number of 



