NOETHUMBERLANB AND DURHAM. 57 



the 65tli, rye to tlie 67tli, and barley to the 70th parallels of 

 latitude, where the annual temperature is 32°, or a little less. 

 They can grow grain in places at least 12° lower in mean tem- 

 perature than we can in England, and to get in Europe a mean 

 of 55° we should have to go to Madrid or Milan. 



But take the polar limits of plants liable to be killed off by 

 frost, and the balance then is altogether in our favour. The 

 holly, for example, is generally nipped where the thermometer 

 falls to Eahrenheit's zero. "With us it is common enough in the 

 lower zone, and extends north as far as Sutherlandshire and the 

 Hebrides. It is restricted to the south-western half of the Con- 

 tinent. In the Scandinavian peninsula it is confined to the South 

 of Norway. It does not enter at all into the Eussian list. Erom 

 Denmark and Holstein its polar limit strikes across the Continent 

 diagonally, by way of Mecklenburg and Austria, to Thrace and 

 Macedonia, and so to the shores of the Black Sea. Our common 

 furze ( Ulex eurojjceus.) is still more decidedly western in its ten- 

 dencies. It avoids Norway, Sweden, Russia, Poland, Austria, 

 Turkey, and Greece altogether. Its polar limit runs across the 

 Continent from Holstein and Mecklenburg to the Tyrol, in a line 

 nearly north and south. The Killarney strawberry-tree {Arbutus 

 unedo) is confined to the South of Erance, Spain, Italy, Greece, 

 and Turkey ; the Connemara heath {Babcecia polifolia) to Spain, 

 Portugal, and the "West of Erance. In general terms, the polar 

 limit of species liable to be killed off by frost runs across Europe, 

 from north-west to south-east, diagonally with the parallels of 

 latitude ; and to sum up, in a single comprehensive pkrase, the 

 relations of the British to the Continental Elora, we may say, 

 that the north limits of the plants, from the nature of the case, 

 as regulated by temperature, radiate from our island like the 

 spokes of a wheel from the axis. 



Area of the Zones of Altitude. — Only two of the Cheviot peaks 

 rise distinctly into the Upper zone, Cheviot itself, which reaches 

 within a few feet of 900 yards above sea-level and the neigh- 

 bouring peak of Hedgehope, which attains nearly 850 yards. 

 Hedgehope is a mere shoulder of hill, but Cheviot has a flat 



