THE GREEN ALGAE OF NORTH AMERICA 195 



wall ; chroniatophore a fine even coating over all the cell wall, 

 often including the dissepiments. Vermont and Mass, to N. Y. 

 Forming light green floccose masses, in still or slow water ; 

 has been collected from May to October, which would seem to 

 indicate less of a spring plant than most species of Microspora. 

 Its very fine filaments with short cells distinguish it quite 

 clearly from our other species. 



Family 2. ULVACEAE. 



Membranaceous, plane, or tubular fronds ; cells uninucleate, 

 with disk-shape chromatophore and one pyrenoid ; asexual re- 

 production by 4-ciliate zoospores (sometimes biciliate ?) ; sexual 

 reproduction by biciliate gametes. 



The membrane is in the form of a tube, a sac, or a flat expan- 

 sion ; in the latter case it may consist of one or two layers of 

 cells ; in the simplest forms there may be merely two rows of 

 cells side by side, or in some parts of the frond, only a single 

 series of cells. Spores and gametes may be formed in any cell 

 of the frond except the lowest cells, which may send down 

 rhizoidal prolongations, uniting to form a stipe. 



Of world-wide distribution ; marine, rarely fresh water plants ; 

 usually gregarious, often growing in great quantities. They 

 are specially plants of the literal zone, occasionally extending 

 down for a short distance into the sublitoral. 



KEY TO THE GENERA OF ULVACEAE. 



T. Frond tubular, rarely of one or two series of cells. 2. 



i. Frond tubular only in the early stages, if ever. 3. 



2. Frond gelatinous ; cells in loosely united longitudinal series. 



2. ILEA. 

 2. Not specially gelatinous; membrane parenchymatous. 



i. ENTEROMORPHA. 



3. Minute ; adherent by the entire lower surface. 5. PROTODERMA. 



3. Larger; adherent only at the base. 4. 



4. Frond of a single layer of cells. 3. MONOSTROMA. 



4. Frond of two layers of cells. 4. UI/VA. 



i. ENTEROMORPHA Link, 1820, p. 5. 



Frond originating in a single series of cells, which by re- 

 peated division form a tubular frond, the membrane of which 

 consists of a single layer of cells ; in some of the simpler species 

 the tubular stage is not reached, and the frond in the adult 

 state consists of two or a few series of cells, united without any 



