THE SELF-FERTILISATION OF PLANTS. 
5 
A very common condition is for the perianth to remain 
scarcely at all opened, so that the stamens are never removed 
from contact with the stigmas. This is the case with small- 
flowering species of Veronica and Cerastium , while Polygonum 
Convolvulus and Hydropiper never, so far as I have observed 
them, open their perianths at all. 
It would seem probable that plants habitually crossed in 
their native country, and well adapted for insect agency, may 
become quite independent of insects in another. Thus the Sweet 
Pea, though crossed in South Europe, is quite self-fertile here, 
as is also the garden Pea. The genus Phaseolus furnishes a 
very remarkable illustration, for while P. vulgaris , the forcing- 
bean, is fully self-fertile, yet P. multijiorus , the scarlet runner, 
is dependent on the visits of humble bees for its full fertility ; 
consequently for many years there have been complaints near 
London of the failure of the crops of scarlet runners, all sorts 
of remedies having been suggested except the right one, which 
is to abandon it altogether and to grow only the kidney bean 
instead. * 
5. Highly self -fertile forms may arise under cultivation. 
This I take from Mr. Darwin’s experiments. In cultivating 
Ipomcea purpurea and Mimulus luteus for several generations 
and comparing the results of crossing and of self-fertilisation, 
in both cases a self-fertilising form appeared which completely 
outstripped its crossed competitors. In the latter case “ the 
self-fertilised plants [of the seventh generation] consisted exclu- 
sively of this variety so it was useless to continue the experi- 
ments.! 
6. Special adaptations occur for self -fertilisation. I have 
already mentioned a few above, such as the perianth closing or 
scarcely opening; and will now describe some taken from genera 
of the natural orders in their usual sequence. 
Eanunculace^e. — In small-flowered Ranunculi , as R. hede- 
raceus , the stamens, instead of spreading away from the stigmas, 
remain arching over them, and so shed their pollen on to the 
stigmas. The same occurs with small-flowered Potentillas. 
Some flowers first spread their stamens away, and then incurve 
them afterwards, as Agrimonia (fig. 33) and Alisma (fig. 52). 
Fumariace^;. — Fumaria officinalis. — Mr. Darwin found this 
to be perfectly self-fertile when insects were excluded. The 
stigmas resemble two horns, each of which is thrust into a 
three-sided chamber formed by the three anthers, which have 
their filaments coherent (figs. 2 and 3). 
Crucifers. — Large-flowered species are adapted for inter- 
* See “ Gardener’s Chronicle,” 1878, p. 561. 
t For further details, see “ Cross and Self-Fertilisation of Plants.” 
