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stick when the latter is turned round, is marked in the record- 

 table; this is repeated until the required number of samples has 

 been obtained. Even without turning the stick it is as a rule easy 

 to see which species occurs within the circle; but if it is doubtful 

 whether a species, which only occurs at the boundary of the surface- 

 unit, grows within the circle or not, then on turning the stick so 

 that the radius points in the direction of the plant in question its 

 place — whether within or outside the circle — will immediately 

 be seen. By employing a circle in the way described above, the 

 single species may, on the whole, be investigated more easily and 

 quickly than by employing the square frame which often hinders 

 the investigation of plants at the periphery of the sample and is, 

 moreover, easily displaced during the investigation. 



As the rod employed as radius is not permanently fixed to 

 the ring but can be screwed off, by employing radii of different 

 lengths the apparatus may also be used in cases where another 

 surface-unit than 1 lio square metre is desired, which in ordinary 

 cases I employed in the determination of the degree of frequency 

 of the species. Thus in the investigation of the plant-density in 

 formations in which the plants stand wide apart as, for instance, 

 in desert regions, it will often be necessary to employ a smaller 

 surface-unit than x /io square metre; thus I found a radius equal to 

 a circle of Vioo square metre useful in the determination of the 

 plant-density in certain parts of the Algerian desert. 



