206 PRACTICAL BOTANY 



This treatment has been an important factor in improving the 

 water within reservoirs used as sources of water supply for 

 many American cities.^ 



189. The brown algae: general characteristics. The blue- 

 green and the green algffi are predominantly fresh-water 

 groups, and are considered the chief representatives of algae. 

 The remaining groups, though almost exclusively salt-water 



Fig. 169. Coleoclwete, a flat-bodied green alga, ■which is a single layer of cells 



in tliiokness. It sometimes "branches extensively 



Alter West 



plants, have such striking characteristics that brief mention 

 of them must be made, and pupils who live near the seacoast 

 will be interested in extendmg this study. The bro'\'\'n algae, 

 or brown seaweeds (^Phceophyceaf), are found along the shores 

 of all the oceans. They grow attached, by means of strong 

 holdfasts, to rocks, piling, or any relatively fixed support that 

 is available. 



1 See "A Method of destroying or preventing the Growth of Algae and 

 Certain Pathogenic Bacteria in Water Supplies," and " Copper as an Algi- 

 cide and Disinfectant in Water Supplies," Bulletins 64 (1904) and 76 (1905) 

 respectively, Bureau of Plant Industry, U. S. Dept. Ayr. 



Whipple, "Microscopy of Drinking "Water," chap. xii. JohnWiley& Sons, 

 New York, 1906. 



