190 CHLOROSPERME^E. 



unfresli water may lie ; nor are they absent from the hot 

 springs of volcanic regions, and are capable of vegetating 

 wherever moisture and a moderate temperature prevail. 

 Thus universally dispersed, they answer many a good pur- 

 pose in the household of nature, and are specially useful in 

 purifying the water in which they live. Unsightly as the 

 green scum may be which they form on its surface, the 

 growth is a renovating process, in which are consumed 

 the deleterious matters and gases which stagnant water ge- 

 nerally contains ; \v r hile, like all green plants, they pour into 

 the atmosphere, during sunshine, oxygen prepared in their 

 delicate tissues from the carbonic acid on which they feed. 

 Comparatively few of them minister to our personal wants, 

 with the exception of a few Ulvse which are used for food, 

 and some of the Confervae which have been employed, 

 where other bandages were unprocurable, for binding frac- 

 tured limbs, &c. 



SYNOPSIS OF THE ORDERS. 



14. SIPHONACE.E. Cells filiform (usually of great length), 



simple, or branched, variously connected ; either one 

 cell forming a filiform frond ; or several intertwined 

 and anastomosing cells, forming a compound frond. 



15. CONFERVACE.E. Cells cylindrical (not of great length), 



truncate, connected into simple or branching, rarely 

 anastomosing filaments. Filaments naked, or sur- 

 rounded by gelatine. 



16. ULVACE^E. Cells many-sided, cohering into a mem- 



branaceous, rarely gelatinous, flat or tubular frond. 



17. OSCILLATORIACE^E. Cells filiform, very long, simple, 

 naked, or invested with mucus, or compacted to- 

 gether into a firmly gelatinous frond. Endochrome 

 annulated. 



18. NOSTOCHACE^E. Cells elliptical or globose, connected 



in gelatinous, moniliform strings. Filaments sepa- 

 rate, or several united together in a gelatinous frond. 



19. (PALMELLACE^E) : Sub-order Hormosporea. Cells el- 

 liptical or globose, separate, contained within mem- 

 branaceous, tubular filaments. 



