166 rV. CLIMATE. 



although not ascending to the same ahsolute elevation. 

 Equality of temperature would have been foirnd if the 

 one species had ascended 40 yards higher in Wales, or if 

 the other species had ascended 40 yards less high in 

 Scotland. CHmato - botanical investigations admit of 

 being facilitated in various other modes through the 

 adoption of an intermediate standard of temperature, into 

 which elevation and latitude can both be resolved. 

 Through this thermometrical representation, those two 

 potent influences on vegetation can be indirectly brought 

 into comparison, and measured against each other ; al- 

 though in a direct manner they are non-comparable. In 

 applying the two tables to phyto-geographical purposes, 

 the intervening altitudes and temperatures can easily be 

 reckoned. Two yards of ascent, or two minutes of lati- 

 tude, are assumed to correspond with one-hundredth 

 (0.01) of a degree of temperature. Conversely, the tenth 

 of a degree of temperature (0.1) will correspond with 

 twenty yards of ascent, or with twenty minutes of a 

 degree in latitude. 



14. Temperature of the Seasons. — The mean tempera- 

 ture for the whole year is now sufficiently understood to 

 be an imperfect measure of climatal influence on the flora 

 and vegetation of a country. In the usual manner of 

 arriving at a mean, low temperatures become reckoned in 

 reduction from the high temperatures ; although in fact 

 the former do not reduce the influence of the latter on 

 plants in a corresponding degree. On comparing two 

 climates, for the one of which the summer and winter 

 temperatures are respectively 60 and 20, while for the 

 other they are respectively 50 and 30, the same mean of 

 40 would probably be obtained for the whole year. But 

 those climates would be adapted to different floras. The 



