THE GREEN ALGAE OF NORTH AMERICA 217 



PROTODERMA Kiitzing, 1843, p. 295. 



Frond a minute disk, closely attached to the substratum, 

 formed originally of radiating, branching filaments, which, ex- 

 cept at the margin, are united to a sub-parenchymatous layer of 

 one or more cells in thickness ; cells with parietal disk-shaped 

 chromatophore and one pyrenoid ; asexual reproduction by 

 aplanospores and by biciliate zoospores with red stigma. 



The proper position of this genus is quite uncertain ; West, 

 1904, places it in the Pleurococcaceae ; Oltmans, 1904, ignores 

 it ; it must be placed somewhere, and in the Ulvaceae is as 

 good a place as any. There is no doubt that immature organ- 

 isms of many kinds have passed under the name of P. viride, 

 but P. marinum is more distinct. 



KEY TO THE SPECIES OF PROTODERMA. 



I. Fresh water. i. P, viride. 



i. Marine. 2. P. marinum. 



i. P. VIRIDE Kiitzing, 1843, p. 295 ; 1856, p. 6, PI. XI, fig. i. 

 Frond pale green, at first circular, later more or less irregular; 

 filaments parenchymatously united in the interior of the disk, 

 free at the margin ; cells in the young frond with thin wall, 

 cylindric to cuneate, 3-6 ft wide, usually 2-3 times as long ; 

 in middle of adult frond 6-8, or even 12 ft wide, 1-2 times as 

 long, spherical, ovoid, or ellipsoid, with thick wall ; zoospores 

 globose to ovoid, 3-3.5 ft diam. ; aplanospores globose to ellip- 

 soid, 2-3 ft diam. Fig. 73. On wood and stones in ponds. 

 Mass., Barbados. Europe. 



" 2. P. MARINUM Reinke, 1889, p. 81 ; P. B.-A., No. LIII. 

 Forming thin coatings of irregular form, composed of angular, 

 parenchymatously united cells, 6-12 // .wide, irregularly placed, 

 except at the margin, there in rather indistinct radiating series. 

 Me. to Conn. Europe. 



Common as a thin green film on pebbles in pools and at low 

 water mark, along the New England coast ; probably elsewhere. 



Family 3. PRASIOLACEAE. 



Filamentous or membranaceous ; cells with star-shape chro- 

 matophore and one pyrenoid ; asexual reproduction by segment- 

 ation of the frond, by akinetes and by aplanospores ; sexual 

 reproduction unknown. Fresh water or marine. 



KEY TO THE GENERA OF PRASIOLACEAE. 



i. Frond normally of a single series of cells, occasionally expanding 

 laterally to two or a few series. i. SCHIZOGONIUM. 



