304 TUFTS COLLEGE STUDIES, VOL. II, No. 3 



A very common spring plant in brooks, etc., varying consid- 

 erably in appearance, but easily recognized. At first it is deep 

 green, but becomes quite pale later in the season, the empty 

 cells remaining after the escape of the zoospores. 



4. D. PLATYZONATA Hazen, 1902, p. 222, PI. XL,!. Loosely 

 tufted, up to 7 cm. long ; branches mostly opposite or whorled, 

 horizontal; fascicles of ramuli at right angles to the stern, dis- 

 tinctly stalked, broadly orbicular in outline, ramuli somewhat 

 symmetrically radiating from the summit of the rachis or its 

 branches, subfusiform, acuminate or setiferous ; cells of the 

 larger branches cylindrical or slightly constricted at the nodes, 

 50-90 /u. diam., i diatn. long or less; chromatophore very wide, 

 nearly or quite filling the cell, often reticular ; ramuli 6-n /u, 

 diam. Vermont, Mass., N. J. 



Though reported from few localities only, this seems to be a 

 quite distinct species, and it will probably be found in other 

 places. 



26. PLEUROCOCCUS Meneghini, 1842, p. 30. 



Cells round, or angular by mutual pressure, dividing in all 

 three directions, remaining attached in irregular masses of up 

 to 32 cells or even more ; chromatophore in form of small grains 

 or united to a disk, with or without a pyrenoid ; zoospores, 

 aplanospores and zoogametes have been reported. 



P. VULGARIS Meneghini, 1842, p. 38, PI. V, fig. i ; Nageli, 

 1848, p. 65, PI. IV. E, fig. 2; P. B.-A., No. 760. Cells 4-6 /* 

 diam., singly spherical but becoming angular when in contact, 

 often 2 to many cells continuing attached. On wood, stone, 

 and brick, in moist or shaded places. Fig. 106. From Greenland 

 south. Europe. 



Probably the nearest to omnipresent of all the algae, as it is 

 found in practically every station, not submerged, where moist- 

 ure is occasionally to be had. It forms the thin green coating 

 found on stone walls, buildings and trees, especially on the 

 north side ; this preference for the north side of trees is usually 

 so marked that one can determine the cardinal points of the 

 compass, except in dense woods. It is- found as far north as 

 Greenland ; whether it has a southern limit, going towards the 

 equator, is not certain. 



It forms a somewhat friable coating in dry weather, becoming 

 gelatinous in rain ; the cells may separate promptly after divid- 



