175 



A LOCAL STUDY IN PLANT DISTRIBUTION. 



By Mr. F. H. DA VET. 



Whichever of the several theories on the distribution 

 of vegetation over the earth may be correct, the tendency of 

 plants to wander and to extend their limits on well defined lines 

 must remain unassailable. Otherwise, in the face of present-day 

 knowledge, it were difficult to account for a similar flora on lands 

 separated from each other by hundreds and sometimes thousands 

 of miles. Thus, although many of the more typical species are 

 absent in the intervening countries, the flora of the Alps is 

 peculiarly arctic, and we very properly conclude that, pushed 

 southwards before the march of the great Ice age, the plants 

 were ultimately stranded on the snow-clad peaks of South 

 Europe, where similar climatic conditions to those enjoyed by 

 their ancestors in the north prevailed, and where, by the self- 

 same restrictions, they have ever since been confined. Similarly 

 the existence of significant groups of plants at places separated 

 from each other b}' wide tracts of water can be explained with 

 no greater cogency than that of a slow movement from a centre, 

 followed by an equally slow but radical re-arrangement of land 

 and water, whereby two extremes of a country have been 

 separated by a boundless main. All these problems, strictly 

 speaking, are the common property of the geologist and botanist, 

 and conjointly they are ever throwing light on the more intricate 

 points. 



But within historic times the wanderings of plants have 

 been greatly complicated by man, and what are known as 

 dissevered species are everj; where found. Since man's in- 

 quisitiveness first led him to foreign nlimes, he has greatly 

 facilitated the distribution of plants, but with this difference : that 

 while, since the dawn of vegetable life, nature has moved slowly 

 and on definite lines, the peregrinations of man have resulted in a 

 distribution sudden, spasmodic, and in many cases antagonistic 

 to the known laws. Let a few examples suffice. It is quite 

 easy to see how a large traffic between two widely separated 

 ports possessing similar climatological and physical features wiU 



