MANUAL OF NATURAL HISTORY. 537 



in Ireland ; the appearance described as "Red 

 Snow " is caused by Protococcus nivalis ; 

 some, as Ulma thermalis, live in hot springs. 



5. Family. — Bond-weeds (Desmidiacese). Bodies 



cylindrical, bipartite ; colour green ; highly 

 mucous, destitute of silex ; multiply by spon- 

 taneous separation ; reproduction by bodies 

 analogous to zoospores. Usually found in 

 cloudy masses near the bottom of permanent 

 old boggy pools. The cells of Bond-weeds 

 contain starch granules. 



6. Family. — Brittle-worts (Diatoinacese). Bodies 



crystalline, angular, fragmentary, very brit- 

 tle ; contain much silex ; composition not 

 binary ; colour dark brown ; multiplication 

 and reproduction as in the last family. In- 

 habit still waters, and boggy places, chiefly 

 in temperate and northern climes. 



