324 FRESH -WATER ALG^E OF THE UNITED STATE*. 



flattened and twisted, with 1-4 or more turns. Breadth ol 

 band (trichome) 2/^; length, when twisted, 75-200 yw. 



Frequent in pool near Minneapolis, Minnesota. 

 Plate CCX, figs. 4, 5. 



Genus 107, SPIKILLUM, Ehrb. 



Trichomes short filiform, imperfectly articulated, spirally 

 twisted, curved snail-shell-like or sub-cylindrical. 



SPIRILLUM UNDULA, ( Muell. ) Ehrb. 



Trichomes short, rather stout ; twisted, making 1-1 2 

 turns, hyaline, distinctly articulate. 



Stagnant pools. 

 Plate CCX, fig. 1. 



Family XIX.CHROOCOCCACEJE. 



Unicellular forms of plant -life, which divide into daughter 

 cells and separate, forming families involved in a mucous, or 

 gelatinous, amorphous thallns. Cells divide and redivide 

 through many generations. 



All the forms of this family are probably mere conditions of 

 development of higher forms. Many of them are thus clearly 

 connected with filamentous plants, as shown on the preceding 

 pages, but others have not been so satisfactorily traced to their 

 origin or to their, destiny ; we therefore retain the older classifi- 

 cation as a means for reference to the various forms. 



Some of these unicellular forms run through many, even to 

 hundreds of generations, before reproducing the original plant; 

 and often before the whole cycle is complete, conditions of tem- 

 perature, moisture or other essential prove adverse to develop- 

 ment, they pass away without reproducing. Artificial cultiva- 

 tion is attended with so many difficulties, little has been gained 

 by many earnest efforts. The life- history of the plants needs to 

 be studied in their own haunts. 



Genus 108, GLOEOTHECE, Naeg. 



Cells cylindrical, oblong, rounded at the ends; cells divide 

 transversely into two nearly spherical daughter cells. The cells 

 occur singly or two or more included in a vesiculiform, colorless 

 tegument. After repeated division, one family with tegument 

 may occur within another enlarged tegument also with family. 



