Page:Transactions of the Natural History Society of Northumberland, Durham, and Newcastle-upon-Tyne (1867).djvu/75

Rh the 65th, rye to the 67th, 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 temperature 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 Fahrenheit'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 Continent. In the Scandinavian peninsula it is confined to the South of Norway. It does not enter at all into the Russian list. From 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 () is still more decidedly western in its tendencies. 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 (') is confined to the South of France, Spain, Italy, Greece, and Turkey; the Connemara heath (') to Spain, Portugal, and the West of France. 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 phrase, the relations of the British to the Continental Flora, 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 neighbouring peak of Hedgehope, which attains nearly 850 yards. Hedgehope is a mere shoulder of hill, but Cheviot has a flat