It forms a large globular mass of light wiry branches
interlaced together, and in autumn decays off at the root, the upper
part drying up. It is then at the mercy of the autumn blast, and it is
said that thousands may sometimes be seen coursing over the plain,
rolling, dancing, and leaping over the slight inequalities, often
looking at a distance like a troop of wild horses. It is not uncommon
for twenty or thirty to become entangled into a mass, and then roll
away, as Mr Kohl says, "like a huge giant in his seven-league boots."
Thousands of them are annually blown into the Black Sea, and here,
once in contact with water, in an instant lose the fantastic grace
belonging to their dry, unsubstantial texture.'
Any one who has seen the feather-like seeds of thistles and dandelions
floating about in the air, will have little difficulty in
comprehending the effect of winds on the distribution of vegetation.
Such seeds, as Mr Henfrey observes, might readily be carried across
Europe by a powerful autumn gale, blowing steadily in one direction.
In physiological language, they belong to the _sporadic_, not to the
_endemic_ class, of which a remarkable instance is afforded in the
flea-bane (_Erigeron canadensis_), a plant which, having found its way
to this side the Atlantic only since the discovery of America, is now
a common weed on the continent of Europe.
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