192 TUFTS COLLEGE; STUDIES, VOL. II, No. 3 



boidal, sharply marked, pyrenoid large. On rock or earth in 

 rapid streams. N. H., Conn. Europe. 



Of about the same size as S.fluitans, but with filaments more 

 distinctly geniculate, cells less easily separable, and especially 

 characterized by the rhizoidal branches. 



6. MICROSPORA Thuret, 1850, p. 221. 



Filaments simple, usually unattached and with no special 

 basal cell ; chromatophore a granular sheet covering the cell 

 wall more or less completely, sometimes with perforations, with- 

 out pyrenoids but with scattered starch granules. Cell wall 

 composed of laminae, so arranged that when the filaments break 

 up for the escape of zoospores, the pieces remain in the shape of 

 cylinders open at both ends, with a cross wall near the middle, 

 the so-called "H section." Asexual reproduction by 2- or 4- 

 ciliate zoospores, i or 2 in a cell ; also by smaller 2-ciliate zo- 

 ospores, formed several in a cell ; both kinds germinating 

 directly ; whether the smaller kind may also act as gametes is 

 uncertain. Aplanospores and akinetes also formed. 



A widely distributed genus of fresh water algae, formerly in- 

 cluded in Conferva, and in some respects allied to the Hetero- 

 kontae, but on the whole nearer to the Ulotrichaceae, by the 

 form of the chromatophore and the chemical nature of the cell 

 contents, as well as by the form of the spores. These characters, 

 however, are of little use except in the study of fresh material. 



KEY TO THE SPECIES OF MICROSPORA. 



i. Cells thick-walled. 2. 



i. Cells thin-walled. 5. 



2. Cells less than 15 M diam. 4. M. pachyderma. 



2. Cells 16 M diaiii. or more. 3. 



3. Cells distinctly swollen. 3. M. Loefgrenii. 



3. Cells cylindrical or nearly so. 4. 



4. Cells 20 M diam., 1-2^ diam. long. 5. M. Wittrockii. 



4. Cells 21-25 M diam., 1-2 diam. long. 2. M. amoena. 



4. Cells 28-33 M diam., 1-2 diam. long. T - M. crassior. 



5. Cells ii M diam. or more. 6. 



5. Cells 10 fj. diam. or less. 7. 



6. Cells 11-14 M diam. , 7 . M. Willeana. 



6. Cells 14-17 /j- diam. 6. M.floccosa. 



7. Cells 5-7 M diam. 10 . M. quadrata. 



7. Cells 7-9.5 M diam. 8. 



8. Cells cylindrical. 8. M. stagnorum. 



8. Cells slightly constricted. 9. M.tumidula^ 



