14 UNIVERSITY OF MISSOURI STUDIES [156 



In every complex plant-society some members are depend- 

 ent upon other members. In the case of parasites this depend- 

 ence is complete, often to the great injury of the host. Vines 

 are dependent upon other plants for support, and trees, thus 

 burdened, become dwarfed, misshapen, or even in course of time 

 are strangled to death. Perhaps in a forest this dependence of 

 some species upon others is best seen. The trees are in control, 

 then follow a succession of shrubs, undershrubs and herbs. 

 Why one species tolerates some species and not others is not 

 clearly known. Partly it may be explained by assuming differ- 

 ent edaphic needs. One plant may take chiefly one element from 

 the soil, another another. Certain plants appear intolerant of all 

 others. Thus the poke (Phytolacca decandra) usually stands 

 with a vacant space around it. 



The presence of a plant in a certain society is occasionally 

 accidental. If a plant is thus out of place, it is often character- 

 ized by a spindling development and by failure to come to 

 flower and fruit. On the other hand occasional individuals are 

 met out of their normal habitat, which in robustness excel those 

 of their congeners growing in normal situations. Thus oaks are 

 very scarce in the beech and maple timberlands, but when found 

 are of gigantic size. The timberland soil appears to be too wet 

 to keep over winter the acorns of most species of oak without 

 rotting. Maples, when transplanted to oak-openings, do well, 

 but their seedlings, because of the dry soil, rarely amount to any- 

 thing. Thus it appears that a suitable environment is afifected. 

 by seeds germinating mainly, or only, under certain favorable 

 conditions. The secret of distribution of many species seems 

 to lie here, and one of the most fertile fields of ecological re- 

 search would be that of testing the germination of seeds in 

 properly equipped laboratories. 



