HOW TO KNOW THE FRESH-WATER ALGAE 



3a Plants coarse and usually rough with lime; ill-smelling (garlic or 

 skunk odor); microscopically showing spherical antheridia lateral 

 and below the oval oogonia; branches with long, corticating colum- 

 nar cells about the main axial cell. Fig. 2 CHAR A 



(Chara corona/a Ziz., however, has no corticating cells.) 



Fig. 2a. Chara canescens Lois.-Des. A portion of a plant in which 

 thorn-like cells arising from the corticating elements give a spiny 

 appearance; b, one node of Chara excelsa Allen showing the oval 

 oogonium above, and the globular antheridium below. 



Most of the species, of which there 

 are many, occurring in North America 

 are world-wide in their distribution. 

 They are to be found usually in streams 

 which are slow-flowing or in lakes in 

 which there is considerable calcium. 

 Some species especially are active in 

 depositing lime upon themselves and 

 are so harsh to the touch as to earn 

 the common name "stone-wort." Marl 

 and other kinds of calcareous deposits 

 may be formed largely by Chara over 

 long periods of time. 



Figure 2 



3b Plant delicate, or if relatively stout, not roughened with lime; dark 

 green, not ill-smelling; microscopically with globular antheridia 

 terminal on a short pedicel within a cluster of branches and above 

 the oogania; main axis not corticated. Fig. 3 NITELLA 



Fig. 3a. Nitella tenuissima (Desv.) Kuetz., habit; b. Nitella ilexilis 

 (L.) C. A. Agardh, portion of plant showing habit of branching. 



Species of Nitella are not seen 

 so often as are the Charas because 

 they usually grow more deeply, 

 thriving in soft water or acid lakes 

 rather than in hard water situa- 

 tions. Some species occur in bog 

 lakes that are darkly stained with 

 humic acids and are collected only 

 by dredging with a plant hook. 

 The plants are greener than Chara 

 and are not encrusted with lime; 

 are not ill-smelling. 



Figure 3 



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