308 COMMON PLANTS. 
one hundred miles, and extending inland to the Dornoch Frith, 
probably seventy miles, cannot be estimated at above one-half the 
number which grows in the South of England. This estimate 
is founded on the Flora Abredonensis (Macgillivray), which in- 
cludes about 630 species ; but deducting stragglers or uncertain 
plants introduced with seeds, or in ballast, or in packings, ete., 
species which rarely prove permanent in the localities where they 
first appear and whence they get rank among the spontaneous 
plants, the proper number of plants near Avericoue is probably 
under 600. The list of Shetland plants amounts to 357: this 
number may also be reduced, though for other reasons. The sum 
of these two lists is, by making the proper deductions, somewhat 
above 900. If this be divided by éwo, the quotient will be about 
450. And if this number be assumed as the amount of species 
spontaneously produced in the two counties of Sutherland and — 
Caithness, containing probably seven thousand square miles and 
two hundred and fifty miles of sea-coast exclusive of estuaries, 
bays, and friths, our estimate will not probably be under the actual 
number. In the six maritime counties on the northern side of 
the English Channel, containing probably nine thousand square 
miles and three hundred miles of sea-coast, we believe the num- 
ber of species is understated at 1000. It is believed that in the 
north of Scotland the number is overstated at 450. 
The following statement will help those who are not conversant 
with such matters to apprehend the fact that the number of species 
is mainly dependent on an increase of temperature. The plants 
of Spitzbergen, all sorts, are about 80; the plants of Greenland 
about 200; the plants of Lapland about 500; the plants of Sweden 
about 1200; those of Germany about 3000, and of France about 
6000. In these enumerations microscopic Fungi and Algee are 
omitted. The phznogamous plants of the Fero Isles amount to 
about 250, Ferns included. The phzenogamous plants of Shet- 
land, with the Ferns and Fern-Allies, are 350. From these data 
it may be pretty near the truth to estimate the vegetation of the 
two Northern counties of Great Britain at 450 or 500 perfect 
plants, including Ferns and the Fern-Allies. The vegetation of 
the counties on the South of England certainly amounts to 1000 
pheenogamous species, including the Ferns and Fern-Allies. Hence 
the law, which chiefly affects the distribution of species, is de- 
duced, ‘that their number increases with the increase of tempera- 
