148 LAKE SUPERIOR. 



over the whole range of forest vegetation throughout both continents. 

 The tabular view of these plants which is given below, will at once 

 show the correspondence and divergence. 



From these facts it might be inferred that the aspect of wooded 

 lands, whether mountainous or level, would be very similar ; that 

 in the northern regions, it compares in every respect with that of 

 high mountain chains. Such an impression is almost universally 

 prevalent among those who are conversant Avith these laws of the 

 geographical distribution of plants, without having had an opportuni- 

 ty actually to compare such countries. It having been my good 

 fortune, after having been for years familiar with the vegetation of 

 the Alps, to visit the northern regions of this continent within the 

 limits of the temperate zone, I was at once struck with the great 

 difference in the general aspect of their vegetation. Indeed, the 

 picturesque impression is an entirely different one, and nevertheless 

 the above-mentioned laws are correct ; b\it the fact is that the 

 changes of mean annual temperature in this country take place at 

 the rate of about 1° of Fahrenheit for every degree of latitude, or 

 for every sixty miles ; or in other AvorOs, as we travel north or south, 

 we reach successively every sixty miles, localities the mean annual 

 temperature of which is 1° Fahrenheit lower or tiigher ; while in 

 the Alps we meet, in ascending or descending, the same change of 

 1° Fahrenheit in mean annual temperature, for every three hundred 

 feet of vertical height ; so that we pass within the narrow limits of 

 between six to seven thousand feet, from the vine-clad shores of the 

 lakes of Northern Italy and Switzerland, to the icy fields of snow- 

 mountains, whose summits are never adorned by vegetation ; a 

 journey which can easily be performed in a single day. Whilst on the 

 other hand from the 40th degree of northern latitude, where the mean 

 annual temperature is nearly the same as that of the foot of the Alps, 

 we find towards the northern pole a diminution of one degree of tem- 

 perature for every degree of latitude, or for every sixty odd miles ; so 

 that we should travel over twenty degrees of latitude, or more than 

 twelve hundred miles from south to north, for instance, from Boston 

 to Hudson's Bay, before passing over the same range of climatic 

 changes as we do in one day in the Alps ; thus causing a narrow ver- 

 tical stripe of Alpine flora to correspond to a broad zone of northern 



