COMMUNITY SUCCESSION AND DEVELOPMENT 



565 



VVoodruflF found that Paramecium aurelia, 

 when introduced into a filtered medium that 

 had contained large numbers of individuals 

 of this species in pure culture, was weak- 

 ened in vitality; similarly, hypotrichs such 

 as Stylonychia pustiilata and Pleurotricha 



mecia were detrimental to paramecia, but 

 that excretion products of hypotrichs were 

 stimulating. Such experiments tended to 

 emphasize the importance of these catabolic 

 products in deteiTnining the hay infusion 

 sequence of protozoan populations. Food 



Fig. 202. Formation of the Chicago area, as the headwaters of the Illinois River system, 

 with the drainage of postglacial Lake Chicago, exposure of the Chicago plain, and the forma- 

 tion of Lake Michigan after the retreat of the Wisconsin ice sheet. (After Salisbury and 

 Alden. ) 



lanceolata, when placed in a filtered 

 medium that had contained many hypo- 

 trichs, manifested a lower vitahty. How- 

 ever, when the paramecia were introduced 

 into the filtered hypotrich medium, the ani- 

 mals had an increased vitality. Woodruff 

 concluded that excretion products of para- 



exhaustion is also a factor. 



On a very much larger scale, both with 

 regard to number of species populations, 

 and diversification of biotic activities and 

 products, the developmental phenomena 

 within the community, and the serai se- 

 quence of communities, are broadly similar 



