LICHENOLOGY OF ICELAND 181 



the reindeer moss entangled with it. The task is simply impossible, 

 the question cannot be answered. The fact cannot be emphasized 

 too sharply, that the figures which have hitherto been given for 

 the areas occupied, and which have been obtained by the method 

 of the above-mentioned authors, do not at all possess the numerical, 

 the mathematical authority which numbers ought to have in order 

 to be useful for purposes of statistical comparison. They are in 

 short an illusion. 



Add to this, that even if the figures for the area occupied could 

 be fixed fairly accurately, that would not give us any great knowledge 

 of the abundance with which the species (or growth-form) in question 

 occurs in an association. A ten-years-old beech-wood will frequently 

 cover as large an area as one of a 100 years, whilst the figures for 

 the area occupied would not give any idea of the enormous diffe- 

 rence as regards masses in the two growths. It is true, anything 

 like this need not be demanded of the figure in question, but then 

 they are not very enlightening in any respect, and are therefore 

 superfluous. 



In connection with the frequency percentage (F. %) (frequency- 

 number), a far better method can be more advantageously employed, 

 a method which science as far as I know has not employed 

 very largely, but which practical men discovered decennia ago. It 

 cannot be employed on excursions, with note-book and squared 

 paper, or on expeditions on horse-back ; it requires a sojourn on 

 the spot, and some patience. It is simply this: The mass of a wood 

 is determined by the forester by its timber-contents in cubicmetres 

 (it may be expressed in terms of weight!); the crop of a rye-field 

 may be given in weight (straw and grain); and quite similarly could 

 the natural vegetation of any place be treated by a man of science: 

 but then it would be necessary to reap the plants, the masses of 

 which are wanted to be known. 



This method has the advantage that - - of course in connection 

 with other descriptive means (frequency-numbers, etc.) - it can be 

 employed to characterize both the whole association, and its in- 

 dividual species. Thus, it is really a valuable piece of information 

 concerning an association, to know, for instance, that on a square 

 metre there grow, on an average, let us say 2 kilograms of plants, 

 while another association perhaps bears 200 kilograms. It must be 

 admitted that this gives quite a striking impression of the plant- 

 producing power in two such localities. I wonder how the tropical 



