THE GEOGRAPHICAL RANGE OF PLANTS. 47 



water of some kind at no great distance beneath the 

 surface. And so a skilled botanist would really be 

 able to tell more about the climate of a place, which 

 he had never seen, on being shown a collection of its 

 plants, than a careless or ill-educated observer, who 

 had resided for a considerable time in the locality : 

 just as a skilled anatomist will construct a close 

 imitation of the whole frame of an extinct animal, on 

 seeing a single important bone which formed part of 

 its body. 



But though the botanist can form an excellent idea 

 respecting climate, etc., from the study of flora; an 

 attempt to guess at the probable character of flora, 

 from the geographical position of a country, might lead 

 to very erroneous conclusions, because the latitude of 

 a place by no means always governs its climate ; as it 

 might, prima facie, be expected to do. 



On turning to the climatic chart of any atlas of 

 physical geography, the examination of it will show that 

 its isothermal lines are here and there curved out of 

 their regular course, on account of being deflected by 

 various local causes. The causes of these variations 

 involve technical questions which will be dealt with as 

 they arise in the course of this work; it will be 

 sufficient for the present to cite the marked deflection 

 of the isotherms over the British Islands, compared 

 with those over Labrador, as a notable instance in 

 point. These wide differences in their mean temperatures 

 are created, as it is now almost universally admitted, 

 by the set of ocean currents. Thus, the British Islands 

 are fully exposed to the influence of the " Gulf Stream," 

 which carries a current of warm water directly upon 

 our coasts; whereas, as the chart of ocean currents 



