182 OLAF GALL0E 



rain-forest, and the lichen-covered heaths of Iceland, would appear 

 when thus compared according to relative weights of produce! It 

 would be extremely interesting to ascertain. 



But also the luxuriance of the individual species or growth- 

 form in an association, would he able to be characterized by this 

 method. It would be very interesting to see, for instance, the result 

 of comparing a piece of Danish heath with an Icelandic heath, in 

 respect to the lichen-vegetation. How many kilograms of lichens 

 each sample-area contains up there in the North and down here 

 in Denmark. 



Unfortunately I have not been able to employ such a "weight"' 

 method in my investigations in Iceland, nor had I at that time 

 considered this matter more closely. But I am convinced that we 

 have here an exceedingly valuable means of description, by which 

 to characterize the difference between the masses, be it of the in- 

 dividual species, the growth-form or the whole association; and, as 

 already mentioned, practical men have long ago used it in pursuit 

 of their object. 



a. The Deserts. 



Large tracts of Iceland have a desert-vegetation, i. e. a very open 

 vegetation consisting of scattered individuals. Where to draw the 

 boundary line between the desert and the closed vegetations, i. e. 

 vegetations which cover the ground completely, is entirely a 

 matter of opinion, and the boundary can only be an artificial one. 

 We may for instance decide, according to Raunkiser's method, 

 to take a large number of equally large sample-areas, and note 

 down their vegetation separately. It will then be seen that many 

 of the areas are entirely devoid of plants, and such areas may be 

 designated (nil)\ and then resolve that a tract of land in which 

 75 % of the sample areas were devoid of vegetation, should be de- 

 signated "desert. But, as already mentioned, whether this "per- 

 centage of voidness" is chosen, or an entirely different one, for the 

 designation "desert," it is and must be a matter of opinion. Such 

 an analysis of "voidness" would be interesting for purposes of 

 comparison, for instance between the Arctic cold-deserts, and the 

 sub-tropical heat-deserts. But such an analysis has not yet been 

 made, nor have the deserts of Iceland been, as yet, sufficiently in- 

 vestigated in this respect. 



In Iceland many different kinds of deserts are found, the best- 



