CHAPTER IV 



SIMPLER PLANTS AND ANIMALS 



Algae and Protozoans 



Water teems with plants and animals invisible to the naked 

 eye but being microscopic they are outside the general 

 scope of this book. Yet it is upon these organisms that the 

 whole aquatic population ultimately depends for its food ; and 

 in a few cases at least one needs no microscope to detect them, 

 for they collect in masses that are conspicuous by their color 

 or odor. Brook beds and water weeds are golden brown with 

 millions of diatoms; the familiar " pond-scum," "green-scum," 

 and the "water-bloom" of ponds and lakes, are made up of 

 microscopic algas. Certain algse make reser\^oir water taste 

 fishy or bitter or make it smell like cucumbers. Pale whitish 

 spots on water-washed stones and fuzzy patches on the legs 

 and backs of water insects are actually colonies of one-celled 

 animals, the beautiful bell-shaped protozoans, Vorticella and 

 Epistylis (Fig. 51). 



Algse. — Fresh water algas are simple plants whose form 

 varies from minute rods, stars, crescents, richly patterned mi- 

 croscopic ribbons, slender filaments, single or branched, to the 

 stoneworts (p. 53), so simply built that they are often classed 

 with algae, yet so large and so much branched that they look 

 like the higher plants. The filamentous algas grow in long 

 threads or filaments, formed of narrow cells, attached to each 

 other end to end, tandem- wise (Fig. 48). Sometimes these 



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