Page:Darwin - The various contrivances by which orchids are fertilized by insects (1877).djvu/311

. IX. occasionally producing capsules under cultivation, likewise come under this head.

Of species which regularly fertilise themselves without any aid and yield full-sized capsules, hardly any case is more striking than that of Ophrys apifera, which was advanced by me in the first edition of this work. To this case may now be added two other European plants, Orchis or Neotinea intacta and Epipactis viridiflora. Two North American species, Gymnadenia tridentata and Platanthera hyperborea appear to be in the same predicament, but whether when self-fertilised they yield a full complement of capsules containing good seeds has not been ascertained. A curious Epidendrum in South Brazil which bears two additional anthers fertilises itself freely by their aid; and Dendrobium cretaceum has been known to produce perfect self-fertilised seeds in a hothouse in England. Lastly, Spiranthes australis and two species of Thelymitra, inhabitants of Australia, come under this same head. No doubt other cases will hereafter be added to this short list of about ten species which it appears can fertilise themselves fully, and of about the same number of species which fertilise themselves imperfectly when insects are excluded.

It deserves especial attention that the flowers of all the above-named self-fertile species still retain various structures which it is impossible to doubt are adapted for insuring cross-fertilisation, though they are now rarely or never brought into play. We may therefore conclude that all these plants are descended from species or varieties which were formerly fertilised by insect-aid. Moreover, several of the genera to which these self-fertile species belong, include other species, which are incapable of self-fertilisation. Thelymitra offers indeed the only instance known to me of two