The reason why : $b a careful collection of many hundreds of reasons for things which, though generally believed, are imperfectly understood. A book of condensed scientific knowledge for the million
John Stuart Mill · en
Lat.
Beech, _Fagus silvatica_ 60 deg. 0 min.
Hard Oak, _Quercus robur_ 61 " 0 "
Common Elm, _Ulmus campestris_ 61 " 0 "
Common Lime, _Tilia communis_ 61 " 0 "
Common Ash, _Fraxinus excelsior_ 62 " 0 "
Fruit trees 63 " 0 "
Hazel, Corylus, _avellana_ 64 " 0 "
Spruce Fir, _Abies excelsa_ 67 " 40 "
Service Tree, _Sorbus aucuparia_ 70 " 0 "
Scotch Fir, _Pinus silvestris_ 70 " 0 "
White Birch, _Betula alba_ 70 " 40 "
Dwarf Birch, _Betula nana_ 71 " 0 "
1238. Thus distinct vegetable regions are observed on passing
from south to north through different climatic zones, defined
as to their limits by the isothermal curves, and not by the
parallels of latitude. Similar changes of vegetation mark a
perpendicular transit through varying climates. A succession of
plants appear on the tropical mountains which rise above the snow
line, corresponding to those which are encountered in mean and
high latitudes. The higher we ascend, the more does the number of
the phænogamic class diminish in proportion to the cryptogamic,
till only members of the latter family are found, whose further
progress upward is arrested by the everlasting snow. The last
lichen met with by Saussure on Mont Blanc, _Silene acaulis_, was
also observed by M. Brevais in the neighbourhood of Bosekop, lat.
69 deg. 58 min. where it was vegetating on the seashore, shaded by
the last pines of Europe.
1239. Isolated mountains display to the best advantage the effort
of climatic change of vegetation.
1240. Etna is divided into three great regions: _La Regione
Culta_, or fertile region; _La Regione Sylvosa_, or woody region;
_La Regione Deserta_, the bare or desert region. But each of
these is susceptible of sub-divisions, defined by the presence of
certain families of plants, forming seven botanical zones.
1. The sub-tropical zone, which does not rise more than 100 feet
above the level of the sea, is characterised by the palm, banana,
Indian fig, sugar-cane, varieties of mimosa and acacia, which with
us are only found in conservatories.
2. The hilly zone, rises about 2,000 feet, characterised by the
orange, lemon, shaddock, maize, cotton, and grape plants.
3. The woody zone lies between the height of 2,000 and 4,000 feet,
where the cork-tree flourishes, several kinds of oak, the maple,
and enormous chestnuts.
4. The zone between the height of 4,000 and 6,000 feet is
distinguished by the beech, Scotch fir, birch, and, among small
plants, by clover, sandwort, chickweed, dock, and plantain.