78 Fresh-water Biology 



Study 13 

 THE LIFE OF ROCK LEDGES* IN A STREAM BED 



Work Program: 



1. A trip to a stream where the water flows over rock ledges, for: 



A. Individual collecting by hand picking. 



B. Hand screen collecting of scrapings and other dislodgments. 



2. A laboratory examination of the catch. 



3. Reading in the Life of Inland Waters, pp. 258 to 261; 363 to 375. 



For Record include: 



1. A sketch map of the ledges. 



2. A diagrammatic profile showing the localization of the principal organisms found. 



3. An annotated list of the organisms collected, arranged under the following headings: 



I. Plants — with notes on size, color, relative abundance, habitat, growth habits, 



etc. 



A. Vascular plants (mosses in crevices, etc.) 



B. Algae — microscopic ones, only when these appear in masses, or color the 



ledges. 



Fringing (sessile) algse. 

 Slime-coat algae. 

 Encrusting algae. 



II. Animals — with notes on size, color, relative abundance, feeding habits, stages 



or ages found, habitat and special adaptations or activities. 



A. Vertebrates — salamanders. 



B. Invertebrates. 



Free ranging: 



Exposed on top of stones. 



Under shelter of stones and in crevices. 

 On vertical face of stones. 

 Sessile. 

 Tube dwellers. 



* A sluice-way of a mill or of a power plant (if flow is permanent) will offer similar conditions. 



