52 FORESTRY OF NORWAY. 
Without homologating these views in any way I avail 
, myself of this as a contribution in aid of my illustration. 
I find it equivalent to an allegation that there have been 
not one but many centres of distribution whence species 
of plants have been dispersed; and I find it at once 
equally convenient, and more in accordance with the views 
Tentertained in regard to the successive development of 
vegetation upon the earth, to look at this fact through 
Forbes’ theory applied to the genus, and through that of 
Schouw applied to species. And I may further remark that 
neither do the views advanced by Forbes and Schouw, nor 
observed facts, necessitate the supposition that the disper- 
sion from a recognised centre took place in a regular 
ever-extending continuous circle. Even the fairy ring to 
which I have alluded, though maintaining generally the 
circular form, shows not a continuous regular circular out- 
line; often it is broken and it assumes something of a 
horse-shoe shape, sometimes it bulges out in the form of an 
oval or an ellipse, and in almost every case the regularity 
of the figures assumed, whatever it may be, is broken by 
void species, or by projections, or by both; and in the 
wider field of nature we find on the ascent of a lofty 
mountain that there are linear zones of different forms of 
vegetation ; while, from the summit, may be seen on the 
plain, well-defined patches of vegetation conformed to 
particular geological formations, curved and winding 
lines of vegetation lining the course of some river or 
streamlet, or it may be, in a well-defined straight line 
traversing the plain, and ascending and crossing the moun- 
tains beyond, covering, but confined to a geological dyke, 
of different material, filling a crack or rent on the super- 
ficial stratum of the ground—a phenomenon of not unfre- 
quent occurrence. 
In view of this the geographical: distribution of all 
plants, including trees—solitary trees, and trees of dense 
forests, continuous or far apart, may occasionally be 
attributed to dispersed seeds having alighted on soil 
favourably conditioned and favourably situated for the 
vegetation of the trees there found. 
