s close allies
insect agency is absolutely required; but in one of these, the
fly-orchis, comparatively very little seed is produced, and
self-fertilisation would therefore be advantageous to it. When
garden-peas were artificially cross-fertilised by Mr. Darwin, it seemed
to do them no good, as the seeds from these crosses produced less
vigorous plants than seed from those which were self-fertilised; a fact
directly opposed to what usually occurs in cross-fertilised plants.

5. As opposed to the theory that there is any absolute need for
cross-fertilisation, it has been urged by Mr. Henslow and others that
many self-fertilised plants are exceptionally vigorous, such as
groundsel, chickweed, sow-thistle, buttercups, and other common weeds;
while most plants of world-wide distribution are self-fertilised, and
these have proved themselves to be best fitted to survive in the battle
of life. More than fifty species of common British plants are very
widely distributed, and all are habitually self-fertilised.[154] That
self-fertilisation has some great advantage is shown by the fact that it
is usually the species which have the smallest and least conspicuous
flowers which have spread widely, while the large and showy flowered
species of the same genera or families, which require insects to
cross-fertilise them, have a much more limited distribution.

6. It is now believed by some botanists that many inconspicuous and
imperfect flowers, including those that are wind-fertilised, such as
plantains, nettles, sedges, and grasses, do not represent primitive or
undeveloped forms, but are degradations from more perfect flowers which
were once adapted to insect fertilisation. In almost every order we find
some plants which have become thus reduced or degraded for wind or
self-fertilisation, as Poterium and Sanguisorba among the Rosaceae;
while this has certainly been the case in the cleistogamic flowers. In
most of the above-mentioned plants there are distinct rudiments of
petals or other floral organs, and as the chief use of these is to
attract insects, they could hardly have existed in primitive
flowers.[155] We know, moreover, that when the petals cease to be
required for the attraction of insects, they rapidly diminish in size,
lose their bright colour or almost wholly disappear.[156]

_Difficulties and Contradictions._

The very bare summary that has now been given of the main facts relating
to the fertilisation of flowers,