rrangements exist
to secure self-fertilisation. Sometimes the corolla closes and brings
the anthers and stigma into contact; in others the anthers cluster round
the stigmas, both maturing together, as in many buttercups, stitchwort
(Stellaria media), sandwort (Spergula), and some willow-herbs
(Epilobium); or they arch over the pistil, as in Galium aparine and
Alisma Plantago. The style is also modified to bring it into contact
with the anthers, as in the dandelion, groundsel, and many other
plants.[151] All these, however, may be occasionally cross-fertilised.

3. In other cases precautions are taken to prevent cross-fertilisation,
as in the numerous cleistogamous or closed flowers. These occur in no
less than fifty-five different genera, belonging to twenty-four natural
orders, and in thirty-two of these genera the normal flowers are
irregular, and have therefore been specially modified for insect
fertilisation.[152] These flowers appear to be degradations of the
normal flowers, and are closed up by various modifications of the petals
or other parts, so that it is impossible for insects to reach the
interior, yet they produce seed in abundance, and are often the chief
means by which the species is continued. Thus, in our common dog-violet
the perfect flowers rarely produce seed, while the rudimentary
cleistogamic flowers do so in abundance. The sweet violet also produces
abundance of seed from its cleistogamic flowers, and few from its
perfect flowers; but in Liguria it produces only perfect flowers which
seed abundantly. No case appears to be known of a plant which has
cleistogamic flowers only, but a small rush (Juncus bufonius) is in this
condition in some parts of Russia, while in other parts perfect flowers
are also produced.[153] Our common henbit dead-nettle (Lamium
amplexicaule) produces cleistogamic flowers, as do also some orchids.
The advantage gained by the plant is great economy of specialised
material, since with very small flowers and very little expenditure of
pollen an abundance of seed is produced.

4. A considerable number of plants which have evidently been specially
modified for insect fertilisation have, by further 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 it