In the white varieties of many
flowers, such as of Digitalis purpurea, Antirrhinum majus, several
species of Dianthus, Phlox, Myosotis, Rhododendron, Pelargonium, Primula
and Petunia, the marks generally persist, whilst the rest of the corolla
has become of a pure white; but this may be due merely to their colour
being more intense and thus less readily obliterated. Sprengel's notion
of the use of these marks as guides appeared to me for a long time
fanciful; for insects, without such aid, readily discover and bite holes
through the nectary from the outside. They also discover the minute
nectar-secreting glands on the stipules and leaves of certain plants.
Moreover, some few plants, such as certain poppies, which are not
nectariferous, have guiding marks; but we might perhaps expect that some
few plants would retain traces of a former nectariferous condition. On
the other hand, these marks are much more common on asymmetrical
flowers, the entrance into which would be apt to puzzle insects, than on
regular flowers. Sir J. Lubbock has also proved that bees readily
distinguish colours, and that they lose much time if the position of
honey which they have once visited be in the least changed. (10/2.
'British Wild Flowers in relation to Insects' 1875 page 44.) The
following case affords, I think, the best evidence that these marks have
really been developed in correlation with the nectary.
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