Many years ago I
suggested that primarily the saccharine matter in nectar was excreted as
a waste product of chemical changes in the sap; and that when the
excretion happened to occur within the envelopes of a flower, it was
utilised for the important object of cross-fertilisation, being
subsequently much increased in quantity and stored in various ways.
(10/45. Nectar was regarded by De Candolle and Dunal as an excretion, as
stated by Martinet in 'Annal des Sc. Nat.' 1872 tome 14 page 211.) This
view is rendered probable by the leaves of some trees excreting, under
certain climatic conditions, without the aid of special glands, a
saccharine fluid, often called honey-dew. This is the case with the
leaves of the lime; for although some authors have disputed the fact, a
most capable judge, Dr. Maxwell Masters, informs me that, after having
heard the discussions on this subject before the Horticultural Society,
he feels no doubt on this head. The leaves, as well as the cut stems, of
the manna ash (Fraxinus ornus) secrete in a like manner saccharine
matter. (10/46. 'Gardeners' Chronicle' 1876 page 242.) According to
Treviranus, so do the upper surfaces of the leaves of Carduus arctioides
during hot weather. Many analogous facts could be given. (10/47. Kurr
'Untersuchungen uber die Bedeutung der Nektarien' 1833 page 115.) There
are, however, a considerable number of plants which bear small glands on
their leaves, petioles, phyllodia, stipules, bracteae, or flower
peduncles, or on the outside of their calyx, and these glands secrete
minute drops of a sweet fluid, which is eagerly sought by sugar-loving
insects, such as ants, hive-bees, and wasps.
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