follows, that the abundance of red clover and wild heart's-ease in a
district will depend on a good supply of cats to kill the mice, which
would otherwise destroy and keep down the humble-bees and prevent them
from fertilising the flowers. A chain of connection has thus been found
between such totally distinct organisms as flesh-eating mammalia and
sweet-smelling flowers, the abundance or scarcity of the one closely
corresponding to that of the other!

The following account of the struggle between trees in the forests of
Denmark, from the researches of M. Hansten-Blangsted, strikingly
illustrates our subject.[8] The chief combatants are the beech and the
birch, the former being everywhere successful in its invasions. Forests
composed wholly of birch are now only found in sterile, sandy tracts;
everywhere else the trees are mixed, and wherever the soil is favourable
the beech rapidly drives out the birch. The latter loses its branches at
the touch of the beech, and devotes all its strength to the upper part
where it towers above the beech. It may live long in this way, but it
succumbs ultimately in the fight--of old age if of nothing else, for the
life of the birch in Denmark is shorter than that of the beech. The
writer believes that light (or rather shade) is the cause of the
superiority of the latter, for it has a greater development of its
branches than the birch, which is more open and thus allows the rays of
the sun to pass through to the soil below, while the tufted, bushy top
of the beech preserves a deep shade at its base. Hardly any young plants
can grow under the beech except its own shoots; and while the beech can
nourish under the shade of the birch, the latter dies immediately under
the beech. The birch has only been saved from total extermination by the
facts that it had possession of the Danish forests long before the beech
ever reached the country, and that certain districts are unfavourable to
the growth of the latter. But wherever the soil has been enriched by the