102 ELEMENTARY BOTANY 
by the presence of mountains. We see the effect of this on 
a large scale when comparing the vegetation of the temperate 
zone with that of the tropical. It is true that Buttercups 
and Anemones, so common in England, do not grow in the 
fields and woods of tropical countries; but they have been 
found on the highest peaks of the mountains of Jamaica ; 
therefore not only has the latitude of a district to be borne 
in mind, but also its altitude. Even in an English county 
the plants growing in a valley will be different from those 
growing on the hills. In Gloucestershire, the Spiny Rest- 
harrow (Ononis spinosa) is found only in the valleys, whilst 
the smaller species without thorns (Onoms arvensis) is found 
on the hills. Even where the same species occurs both on the 
hills and in the valleys its growth is different; thus the 
pyramidal Orchis growing in the valley of the Severn is 
larger, its blossoms further apart and paler than the same 
species growing on the Cotswolds. | 
Nature ofthe lhe nature of the soil is another very im- 
Soil. portant factor in the distribution of plants ; some 
will thrive only on limestone, others cannot live on it; some 
require sand, and so on. Thus the Foxglove is found in 
Gloucestershire only in the western part of the county, 
because there strips of red sandstone occur. In the bogs of 
the same region is found the Sundew, which cannot thrive 
where lime is present. : 
Rainfall, The rainfall, direction of the watershed, 
Rivers, ete. nature of the rivers, whether tidal or not, all 
have their influence on the flora of a district. Comparing, for 
instance, two counties which are practically inland, if one 
has a tidal river and the other has not, sea plants, like Sea 
Lavender, Sea Aster, Sea Thrift, will be found in the one and 
absent in the other. 
Direction of The direction of the wind is a very important 
the Wind. —_ consideration, for seeds are dispersed largely by 
wind. It accounts for such facts as the occurrence of the 
same plants several miles apart from each other, and not in 
the intervening districts. 
