with each other. In the orange tribe, Gallesio (15/15. 'Teoria della
Riproduzione Vegetal' 1816 page 12.) remarks that the amelioration of the
various kinds is checked by their continual and almost regular crossing. So it
is with numerous other plants.

On the other hand, some cultivated plants rarely or never intercross, for
instance, the common pea and sweet-pea (Lathyrus odoratus); yet their flowers
are certainly adapted for cross fertilisation. The varieties of the tomato and
aubergine (Solanum) and the pimenta (Pimenta vulgaris?) are said (15/16.
Verlot 'Des Varietes' 1865 page 72.) never to cross, even when growing
alongside one another. But it should be observed that these are all exotic
plants, and we do not know how they would behave in their native country when
visited by the proper insects. With respect to the common pea, I have
ascertained that it is rarely crossed in this country owing to premature
fertilisation. There exist, however, some plants which under their natural
conditions appear to be always self-fertilised, such as the Bee Ophrys (Ophrys
apifera) and a few other Orchids; yet these plants exhibit the plainest
adaptations for cross-fertilisation. Again, some few plants are believed to
produce only closed flowers, called cleistogene, which cannot possibly be
crossed. This was long thought to be the case with the Leersia oryzoides
(15/17. Duval Jouve 'Bull. Soc. Bot. de France' tome 10 1863 page 194. With
respect to the perfect flowers setting seed see Dr. Ascherson in 'Bot.
Zeitung' 1864 page 350.), but this grass is now known occasionally to produce
perfect flowers, which set seed.

Although some plants, both indigenous and naturalised, rarely or never produce
flowers, or if they flower never produce seeds, yet no one doubts that
phanerogamic plants are adapted to produce flowers, and the flowers to produce
seed. When they fail, we believe that such plants under different conditions
would perform their proper function, or that they formerly did so, and will do