204 



PRACTICAL BOTANY 



form somewhat like Pleuroeoccus, is frequently found in stag- 

 nant water. It sometimes grows so luxuriantly in barnyard 

 and roadside pools as to give the water a bright green appear- 

 ance, and its resting spores may impart -a dark red color to the 



drying pools in which the plants 

 have flourished. Of the near rela- 

 tives of Spirogyra there are several 

 kinds, some of which are Zygnema 

 )P %.(Fig, 16), Mesocarpus (Fig. 167), 



, and the desmids 

 (Fig. 168). The 

 desmids are pe- 

 culiarly fantastic 

 forms, one-celled, 

 but often found 

 in colonies. They 

 usually appear in 

 stagnant waters. 

 As in Spirogyra, 

 these plants repro- 

 duce themselves 

 by formation of 

 zygospores. Con- 

 ferva, which re- 

 sembles Ulothrix 

 (see Fig. 159), is 

 fairly abundant in 

 ponds and along 

 margins of lakes. 

 Draparnaldia is a 



branching form (Fig. 160) which resembles Cladophora and 

 Vaucheria ; Ulva, or sea lettuce, is a peculiar large salt-water 

 form ; while Coleochcete (Fig. 169) is a disk-like or plate-like 

 form. Ohara, or stonewort (Fig. 170), is a complex alga that 

 is found in great abundance upon the bottom of shallow lakes 

 and streams throughout the continent. It has a heavy coating 



FIG. 167. Mesocarpus 



c, conjugating cells which have bent toward one another 



and are producing conjugating tubes; p, a start toward 



conjugation with a third plant. Greatly enlarged 



