Delpino argues
that such glands ought not to be considered as excretory, because if
they were so, they would be present in every species; but I cannot see
much force in this argument, as the leaves of some plants excrete sugar
only during certain states of the weather. That in some cases the
secretion serves to attract insects as defenders of the plant, and may
have been developed to a high degree for this special purpose, I have
not the least doubt, from the observations of Delpino, and more
especially from those of Mr. Belt on Acacia sphaerocephala, and on
passion-flowers. This acacia likewise produces, as an additional
attraction to ants, small bodies containing much oil and protoplasm, and
analogous bodies are developed by a Cecropia for the same purpose, as
described by Fritz Muller. (10/50. Mr. Belt 'The Naturalist in
Nicaragua' 1874 page 218, has given a most interesting account of the
paramount importance of ants as defenders of the above Acacia. With
respect to the Cecropia see 'Nature' 1876 page 304. My son Francis has
described the microscopical structure and development of these wonderful
food-bodies in a paper read before the Linnean Society.)
The excretion of a sweet fluid by glands seated outside of a flower is
rarely utilised as a means for cross-fertilisation by the aid of
insects; but this occurs with the bracteae of the Marcgraviaceae, as the
late Dr.
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