1 86 BOTANICAL GAZETTE [February 



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number (25-50) of small unit areas of the vegetation, selected at random or 

 according to fixed plans, and outlined by the revolution of a metal radius of 

 determined length attached to a walking stick. 13 The convenient size of these 

 unit areas appears to be 0.1 sq. m., and the frequency with which a given 

 species appears in such areas determines its valence, frequency percentage, or 

 frequency coefficient. Emphasis is placed upon the fact that in an undis- 

 • turbed area the vegetation will eventually come to a practically complete 

 equilibrium with the factors of the habitat, and will be composed of the species 

 of the region best fitted to exist under such conditions. Raunkiaer therefore 

 defines his "formation" as " essentially homogeneous from a floristic point of 

 view," that is, homogeneous as to the dominant species or the species showing 

 the highest frequency coefficients. Such a statistical method permits the 

 quantitative comparison of similar plant communities and their more exact 

 delimination. 



It is interesting to note as the results of the use of such statistical methods, 

 principally the examination of many plant communities involving the deter- 

 mination of over 8000 coefficients, that 55 per cent of the species have coeffi- 

 cients ranging from 1 to 20, 15 per cent from 81 to 100, 14 per cent from 21 

 to 40, 9 per cent from 61 to 80, and 3 per cent from 41 to 60. In other words, 

 the least frequent species in the communities studied were most numerous, 

 while the most frequent came second in order of number of species, with a 

 much smaller number showing moderate abundance. These phenomena the 

 author expresses in the form of a law. "In a formation in a relative state of 

 equilibrium what allows one or more species to prosper at the expense of their 

 neighbors is the fact that the dominant species are better adapted to live under 

 the conditions existing within the formation of which they are a part and by 

 their community life (' concurrence vitale ') they prevent the other species from 

 equaling them in frequency. But however well equipped they may be for 

 such community life, they are not able to preverft other species, widely dis- 

 seminated but fewer in individuals, from entering the formation and occupying 

 portions that for any reason whatever may have been left unoccupied by the 

 dominant species. Thus we see that there is a much larger number of the 

 least frequent species." • 



For the further analysis of vegetation Raunkiaer describes a method of 

 arriving at the area occupied by each species in the community. This is 

 accomplished by the study of unit areas similar to those employed in the 

 determination of frequency; indeed the two could be done simultaneously. 

 To assist in readily determining the portion of the area occupied by the areal 

 parts of a species he adds a series of radii of determined length to the one 

 already affixed at right angles to the walking stick. These are so spaced that 

 they divide the circular unit area into fifths and tenths, so that by their aid 



** Raunkiaer, C, Measuring apparatus for investigations of plant formations. 

 Bot. Tidskr. 33 -45-48. 1012. 



