XI 
THE SPECIAL COLOURS OF PLANTS 
323 
modification, become quite self-fertile. This is the case with 
the garden-pea, and also with our beautiful bee-orchis, in which 
the pollen-masses constantly fall on to the stigmas, and the 
flower, being thus self-fertilised, produces abundance of capsules 
and of seed. Yet in many of its close allies insect agency is 
absolutely required; but in one of these, the fly-orchis, com¬ 
paratively 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-fer¬ 
tilised 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, duckweed, 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. 1 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 in¬ 
conspicuous and imperfect flowers, including those that are 
wind-fertilised, such as plantains, nettles, sedges, and grasses, 
do not represent primitive or undeveloped foians, 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, 
1 Henslow’s “ Self-Fertilisation,” Trans. Linn. Soc. Second series, Botany, 
vol. i. p. 391. 
