THE GREEN ALGAE OF NORTH AMERICA 195 



wall ; chromatophore 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 UI/VACEAE. 



i. 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 



