vegetative and productive power o f such a climate is solely derived
from the summer, and is not in the least regulated by the cold of
winter. Provided always, as is the case, that the plants o f the country,
such of them as are not covered up by the snow, are hardy enough
to withstand the rigour of winter without being destroyed. Let us
now consider the vegetative power of the climate o f Lapland, which
constitutes one of the most curious and important particulars respecting
the climate.
The term climate in common language includes not only the temperature
o f the air, but the notion likewise o f vegetation. Nobody
would say that the climate of Enontekis is 54-° colder than the climate
of Mageroa, provided he were told that the former is covered with
wood, while the latter is scarcely capable of supporting any vegetation
at all. Y e t 5-i° is the difference between the mean temperature of the
air in the two places, and the difference is in favour of Mageroa. The
summer temperature in fact constitutes climate as far as vegegation is
concerned; because upon it depends the power of the country to produce
vegetables. Both at Lpsala and at Enontekis it is necessary that
the thermometer be at 39° before the ice gets loose from the hanks,
and is carried by the rivers into the sea. It must be at 464-:! before
barley can be sown, and it must reach 534° before the birch puts forth
its leaves. In all those countries where the mean heat of summer does
not amount to 53-4° the birch cannot vegetate, even though the temperature
o f the winter be ever so mild. This is the case at the . north
Cape, and likewise at St. Gothard, in Switzerland. Other plants require
a long rather than a hot summer. . Wherever the mean temperature
of the summer for three.months does not amount to 4 7 , ■ there
big will not ripen. This happens long before we reach Enontekis.
Yet there are various trees which are satisfied with the short and warm
summer of that country; for the birch and various species.of willow
vegetate and grow well even in more inhospitable parts of Lapland
than Enontekis. The pines require a long rather than a warm summer;
hence in Switzerland they ascend much, higher than the bifch.
But the very contrary happens in Lapland, where the summer is much
shorter than in Switzerland. We know likewise that in the Andes the
mean temperature during all the months of the year is wonderfully
equable. Hence all the trees that require a hot rather than a long
summer cease to vegetate there much farther below the line of perpetual
congelation than in Lapland ; while barley and other species of
corn, which are satisfied with a temperature of 47° or 48°, provided it
continue for a considerable time, advance much nearer the line o f perpetual
congelation than any tree whatever. From these observations
it is evident that we can determine a climate much more accurately
from the plants that grow in it than from any other mode.
Small plants in all parts of the world are found to vegetate in places
where the summer temperature is too low for trees. Indeed the want
o f sufficient summer heat is the reason why trees do not grow in alpine
regions, and not the violence o f winds nor the rigour of winter. The
birch affords a good evidence o f this, .where it grows upon the borders
of the alpine regions. The inhabitants consider the summer to be a
good one when the buds o f the birch put forth five leaves, and when
the buds only put forth three leaves they conceive the summer to be
bad. Now in the borders of those alpine regions, where it is just
ceasing to vegetate, it never puts forth more than three leaves, and the
branches are very knotty. The hetula nana never puts out more than
three leaves from a bud ; and as these leaves are small, they come to
maturity in three or four weeks, provided the temperature be sufficiently
high ; and therefore in the Lapland Alps this tree ascends higher
than any other ; but in Switzerland it does not even approach the Alps,
because the summer heat is not sufficient for its vegetation.
In this way we may explain the progress o f vegetation towards the
Alps. That different plants follow diffèrent progressions in different
countries depends upon the heat or the length o f the summer. Where
the summer is hot, but short, certain plants, as the birch, will thrive ;
where the summer is long, but cold, other plants, as barley, will vegetate
successfully. Hence it is of the utmost importance to observe the
places where various plants cease to grow, not merely as an object o f
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