1M) OLAF (1AI.L0E 



value varies greatly, and at the outset we may say that, for an 

 exhaustive description, it is necessary to use several methods. Na- 

 ture is too many-sided to be described in a few words, or by 

 tabular methods. 



Among the chief methods may be mentioned Raunkiaer's 

 valency-method (Raunkiser, 1916) which consists in the following: 

 In an association a number of equally large sample-areas (e. g. 1 /io 

 square metre) are demarcated, with equally large intermediate spaces 

 between them, and the vegetation in them is investigated. Any 

 plant-species (or any growth-form) which occurs in all the sample- 

 areas is said to have the frequency-percentage (F. /o) 100, in half 

 of the samples F. % 50, etc. 



By means of this method an idea is obtained of the frequency 

 of the occurrence of the species (or growth-form) in the association. 



Investigators have also tried to express by figures the size of 

 the space occupied by each single species, (or growth-form) in the 

 area of the association; the mode of procedure is similar to that 

 used in the determination of frequency, in so far that samples are 

 taken, the area occupied by every single species in the sample is 

 determined, and on the basis of this, the total amount of area 

 occupied by the species in the whole association, is calculated. 

 Lagerberg, Raunkiser, H. E. Petersen and C. Ferdinandsen 

 recommend and employ this method (see these authors in the 

 Bibliography). 



It is evident that it is very much to be wished, that we could 

 give figures, which would be reliable for the areas occupied by the 

 individual species. In the mean time it must be said, that the 

 attempts made by the above-mentioned authors, to make such cal- 

 culations, have proved an utter failure, and are quite worthless al- 

 though, unfortunately, we must expect the method to be in vogue 

 for some lime, and to be employed by others. 



The unreliability of the results obtained by this method, is due 

 to the following fact: Even if we take a sample, ever so small, it 

 is impossible to decide with any certainty how large a part of it 

 is occupied by this or that species, unless it actually happens that 

 only one species occurs in the sample. As soon as there are several 

 species more or less entangled in each other, the conditions per- 

 taining to the space occupied, are incapable of accurate description. 

 How are we to determine, for instance, in a Danish C//H/ia-healh, 

 how much of a sample is occupied by Calluna, and how much by 



