6 CLIMATE AND SPECIES. 
of any area. It should be added that in two or three points 
this theory has received elucidation in recent publications, viz., 
Mr. Baker’s “ Flora of the Lake District,” pages 3 to 6, and in 
an interesting paper by Mr. 8. M. Macvicar in “Journal of 
Botany,’ 1898, 82 sqq. It is there pointed out that the real 
determining factor in the distinguishing of zones is temperature, 
and further that the influence of temperature is itself modified 
by that of the surface conditions; that is, by the presence or 
otherwise of suitable stations. Thus in some cases boreal species 
are found ascending higher than their normal zone when there 
are suitable rocks or soil, and in others not reaching their usual 
elevation, for want of the same. 
In Derbyshire we have three zones exemplified, the two 
upper zones of the Agrarian, and the lowest zone of the Arctic 
region. The lowest zone of the Agrarian is not, I consider, 
admissible within our boundaries, for although Mr. Watson lays 
down the Trent as the northern limit of this zone, yet of the 
three species occurring which belong to it alone, Rubia has 
evidently ascended above its normal elevation, Clematis is very 
doubtfully indigenous, and (Wnanthe fluviatilis is scarcely a test 
plant of a zone. Beginning, then, with our lowest—the mid- 
agrarian zone—of which the characteristic species are Rhamnus 
catharticus and Cornus sanguinea, it may be subdivided with us 
into two; first a lower, milder, warmer area south and east of 
Derby, and from Burton along the course of the Trent, ranging 
from about 90 feet to 250 feet, in which the following plants 
reach their upper limit :—Dzplotaris muralis, Geranium pusillum, 
Vicia lathyroides, Bryonia dioica, @nanthe flurratilis, Dipsacus 
silvestris, Filago minima, Hottonia palustris, Utriewlaria 
vulgaris, Polygonum minus, Rumer maritimus and R. pulcher, 
Calamagrostris lanceolata, Festuca Myurus; and second a higher 
area, comprising the valleys and hillsides from 250 feet to 
1,050 feet in the central and south-western part of the County, 
with Huonymus europeus, Rhamnus catharticus, Acer campestre,: 
Convolvulus sepium, Tamus communis as characteristic species, 
which reach their limit here. 
