Page:Transactions of the Natural History Society of Northumberland, Durham, and Newcastle-upon-Tyne (1867).djvu/325

Rh agency than to be genuine aborigines, but it is of course impossible to draw the line between the two classes with any precision. In this eighty-nine we include sixty-three well-established weeds of cultivated ground, and twenty-six which are either trees or plants likely to have been introduced through garden cultivation.

3. — Classing the plants of the two counties according to the types of distribution of the Cybele Britannica, we obtain the following result:—

4. — If we arrange the plants of Britain on the basis of this last table in three principal geographical classes, according as they are distributed over its whole extent, or shew a northern or southern tendency, we shall of course find the characteristic peculiarities of the botany of the different parts of the island as compared with one another, in the absence or presence of the plants of the two last classes. The characteristic of the North of England is that it yields a fair proportion of both of them. In Northumberland and Durham we have one hundred and fourteen out of the two hundred and thirty-eight northern and montane plants, and two hundred and eighty-two out of the six hundred and six comparatively southern species. Of the eighteen botanical provinces defined in the Cybele the richest in number of species are those of the south-east of England. The Thames province, which includes Kent, Surrey, Berks, Oxford, Bucks, Middlesex, Herts, and Essex, an area of 7000 square miles, yields one thousand and fifty-one species. The Channel province, which