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PLANT PHYSIOLOGY AND ECOLOGY 



to which the seeds may be carried. The one is characteristic of 

 fleshy fruits, and the other of nut fruits. 



4. ^lan (brotochores). Distribution by man has no necessary 

 connection with mobility. It acts through great distances and over 

 immense areas, as well as near at hand. It may be intentional, as 

 in the case of cultivated plants, or unintentional, as in thousands 

 of native or foreign species. No other disseminating agent can 



Fig. 99. A plant of an aster established near the top of a tall chimney 

 through the agency of the wind. 



compare with man in respect to the amount or distance of migra- 

 tion. 



5. Gravity (clitochores) . Gravity is an agent of migration in 

 hilly and mountain regions, where seeds and fruits regularly reach 

 lower positions, either by falling from cliff or rock, or, more fre- 

 quently, by the breaking away and rolling down of rock or soil 

 masses. Dissemination by this method is necessarily local, though 



