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The degree of frequency of any individual species is determined 

 according to how many of a certain number of samples it was, in 

 which the species occurred; this degree of frequency may be ex- 

 pressed by the figures of a scale agreed upon beforehand. The 

 number of the samples necessary to the determination of the degree 

 of frequency is dependent on the invariability of the result of the 

 investigations; thus, if the result arrived at by the investigation of 

 a certain number of samples is practically unchanged however much 

 the number of the samples is increased, the number first employed 

 was sufficient. On employing this method in the investigation of a 

 large number of different formations it has been proved that as a 

 rule 50 samples are sufficient if 1 lio square metre is used as a 

 surface-unit. 



To delimit the different samples I originally employed a square 

 frame which, as already mentioned, included an area of 1 /io square 

 metre; this frame was thrown at random in the formations which 

 was to be investigated, then every species which occurred within 

 the frame was noted down, i. e. a mark (for instance, a vertical 

 stroke) was made in the plant-list in question; then the frame was 

 thrown again and the species which occurred within the frame in 

 the new place were marked as before: this was repeated a certain 

 number of times, usually 50 times, as mentioned above. 



For various reasons, e. g. for the determination of the density 

 of the vegetation, it is of interest afterwards to be able to scruti- 

 nize the result of every simple throw, which should, therefore, 

 have its fixed place in the table recording the investigation. 



The degree of frequency can be expressed in various ways. 

 I find that the easiest method is simply to use the number of 

 marks gained by each particular species in the investigation of the 

 50 samples as an expression of the degree of frequency of the 

 species in the formation in question. But, of course, other scales 

 of frequency might also be employed, for instance, 1 — 10 or, as I 

 should prefer, 1 — 5; in the latter case those species, which obtain 

 1—10 marks in the investigation of the 50 samples will be awarded 

 the degree of frequency 1; those that obtain 11 — 20 marks, a fre- 

 quency 2, etc.; 41 — 50 is equivalent to a degree of frequency 5. 

 Or the degree of frequency may be expressed by the percentage of 

 the samples in which a particular species has been found; a species 

 which has been found in 40 out of 50 samples is then awarded 

 the degree of frequency 80. 



