tion of its body the anthers in a young flower, and the stigma in an older; it thus brushes the pollen from the anthers and
conveys it to the stigma, and so the pollen of the younger
flower fertilises the older.' It has been already said, that Sprengel was also acquainted with the opposite form of dichogamy; and the result of his explanation of both kinds is the
conclusion, that some flowers can only be fertilised by the aid
of insects, and he adds that some cases are to be found, in
which the arrangements in the flower are of such a nature as
to involve the injury and even the death of the insect that
gives its services. Further on he tells us, that all flowers, 'which are without a proper corolla and have no calyx of any
importance in its place, are destitute of nectar, and are not
fertilised by insects but by some mechanical means, as by the
wind, which either blows the pollen from the anthers on to
the stigmas, or shakes the plant or the flower and makes the
pollen fall from the anthers on to the stigmas.' He observes,
that such flowers always produce a light pollen and in large
quantities, whereas the pollen of nectar-bearing plants is heavy.
Then he shows how his principles explain all the physiological
characters of flowers, position, size, colour, smell, form, time of flowering and the like.
Sprengel set out with the idea, that the nectar and certain arrangements in flowers are expressly intended for the service of insects; but his investigations led him ultimately to the conclusion, that insects themselves serve not only to effect the fertilisation of plants generally, but also in all ordinary cases to bring about the crossing of different flowers of the same plant or of different plants of the same species. There remained a question, which from Sprengel's strictly teleological point of view especially required an answer, what was the object of this crossing of flowers or individual plants? Sprangel was content, as we have seen, with simply stating the fact, and with saying, that nature apparently did not choose that any flower should be fertilised by its own pollen. Who would
