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



tatively, the divisions each sending down root-like prolongations. 

 Sexual reproduction by biciliate gametes, formed several to 

 many in a cell, and by conjugation forming a star-shaped 

 zygote, which after a period of rest develops directly to a normal 

 plant. Under certain conditions the gametes do not conjugate, 

 but assume a rounded form, and soon develop to a normal plant. 

 Asexual reproduction by aplanospores formed many in a cell, 

 often colored red with haematochrome ; these have a longer or 

 shoiter resting period, and either develop directly to normal 

 plants, or produce biciliate gametes, similar to those already 

 described. Only one species. 



P. BOTRYOIDES (Kiitz.) Klebs, 1896, p. 222, PI. I, figs. 1-16, 

 P. B.-A., No. 1268 ; Botrydinm granidatnm Rostafinski and 

 \yoronin, 1877, p. 16 in part, PI. V ; Tilden, American Algae, 

 No. 45, in part. Exposed part ^2-5 mm. diam., vegetative di- 

 vision usually into 4-16 cells; zoospores 15-20X5-8^; aplano- 

 spores globose, about 40 //. diam'. On moist ground, especially 

 clay. Fig. 38. Conn., Minn., Cal. Europe. 



This species seems to occur usually in connection with one or 

 both species of Botrydinm, and was described by Rostafinski 

 and Woronin as a condition of that genus. In Miss Tilden's 

 specimens it is in company with B. Wallrothii Kiitz. 



Family 3. HALOSPHAERACEAE. 



Unicellular, spherical, plankton algae of relatively large size ; 

 cell thin-walled, uninucleate, with numerous disk-shaped chro- 

 matophores, usually with pyrenoids. Asexual reproduction by 

 obconic zoospores, or by aplanospores. Fresh water and marine. 



KEY TO THE GENERA OF HALOSPHAERACEAE. 



i. Reproduction by numerous aplanospores. 2. EXCENTROSPHAERA. 

 t. Reproduction by division into 2, rarely 4 cells. 



i. EREMOSPHAERA. 



i. EREMOSPHAERA De Bary, 1858, p. 56. 



Cells solitary, uninucleate, free, large, spherical, with num- 

 erous small chromatophores, either parietal or radiating from 

 the center, with 1-4 pyrenoids; cell wall normally^thin, but 

 sometimes gelatinizing freely ; cells often showing several con- 

 centric walls ; cells dividing into 2, rarely 4 cells, freed by the 

 breaking up of the mother cell wall ; resting cells with thick 

 walls and brick-red contents, ultimately resuming the normal 

 condition. Fresh water. Only one species. 



E. VIRIDIS De Bary, 1858, p, 56, PI. VIII, fig. 26; Wolle, 

 1887, p. 200, Pl.XCLXVII, fig. ii ; P. B.-A., No. 458. Fig. 39. 



