798 



intended that localities for the species do certainly occur under the 

 mathematical lines of 50° and 53°, but simply that they occur more 

 southerly than 51°, more northerly than 52°. The native localities of 

 the Clematis all occur under the 51st, 52nd, and 53rd degrees ; and 

 thus the first lines which indicate whole degrees, south and north of 

 the extreme localities, are those of 50° and 53°. Some little uncer- 

 tainty will arise occasionally in applying the figures. For example, 

 the parallel of 59° crosses the Orkney Isles, and there are no records 

 adequate to show which of the Orkney species, if any, do not pass to 

 the northward of that line. In this uncertainty, to distinguish those 

 of Orkney from the species which cease in Sutherland or Caithness, 

 all the former are assumed to be bounded northward by the line of 

 60°. At the other end of Britain, the Cornish species are assumed to 

 be all on the north side of 50°, notwithstanding that the Lizard Point 

 is rather short of that line. Of the Scilly flora, almost nothing is yet 

 known; and hence the parallel of 49° is scarcely used in this work. 



" The types of distribution have been explained in former pages of 

 this volume. It may be as well again to remind those who use this 

 work, that such a mode of grouping species, though founded upon 

 fact, can be only a rough view or approximation to nature ; many of 

 the species being so intermediate in the character of their distribution, 

 as to render it doubtful, if not optional, to which of the types they 

 should be referred. The first species of the series, the conspicuous 

 Clematis, is an example of a doubtful type ; while the second one, 

 the easily overlooked Thalictrum alpinum, is an unquestionable ex- 

 ample of the Highland type. 



" The sixth line gives the region or regions, and the zonal range of 

 the species. The regions and zones have also been explained in 

 former pages. In the case of species which occur in both the Arctic 

 and Agrarian zones, an abbreviation is made into the two initial letters 

 * A. A.' The zonal range is indicated by naming the highest and 

 lowest zones inhabited by the species, if growing in more than one 

 of them, as is more usually the case. 



" The seventh line is intended to show the lowest ascertained limit 

 of the species. Comparatively few British species are wholly restricted 

 to localities much above the level of the shores. Hence, for the 

 greater number, the lower limits are indicated with reference to the 

 most southerly provinces within which they descend nearly or quite to 

 the sea level. The expression ' coast level ' is not to be construed as 

 meaning the actual level of the tides, but simply low situations not 

 much above the sea. For species which do not descend to the coast 



