THE STRUCTURAL CHARACTERfSTfCS OF THE COMMUNITY 35 



odorata or Carex pilosa in the herb layer may each reach a cover of 



5. 



When this combined estimate is used, the gregariousness (sociabil- 

 ity) should also be given. 



Whereas in small areas (1 to 2 sq. m. or less) the estimate of cover is 

 often sufficient, in larger areas, and especially in less homogeneous 

 areas, the combined estimate can be used to advantage. Besides, from 

 the combined estimate the cover can mostly be deduced, since the 



Fig. 14.— Corfusa matthioli (Soc. 2) between Alnus viridis shrubs Lower Engadin, Swiss 

 Alps. {Photo by Hoffmann-Grobety.) 



figures + and 1 taken together correspond to cover 1, and number 2 

 of the combined estimate corresponds with cover except in case of a 

 species with many very small individuals which covers less than one- 

 twentieth of the area (many therophytes of the Mediterranean 

 communities). 



Sociability, Gregariousness {Soziahilitdt) , and Dispersion. — After 

 Willdenow (1798) first took notice of the difference in the gregarious- 

 ness of plants, Heer (1835, p. 49) directed attention to the grouping of 

 species, "whether the species stand close together in mass formation 



