surface soon became closely inflected; but the dorsal ones did not
move, though the leaves were left in the solution for many hours, and
though their glands from their blackened colour had obviously absorbed
some of the salt. Rather young leaves should be selected for such
trials, for the dorsal tentacles, as they grow old and begin to wither,
often spontaneously incline towards the middle of the leaf. If these
tentacles had possessed the power of movement, they would not have been
thus rendered more serviceable to the plant; for they are not long
enough to bend round the margin of the leaf so as to reach an insect
caught on the upper surface, Nor would it have been of any use if these
tentacles could have [page 284] moved towards the middle of the lower
surface, for there are no viscid glands there by which insects can be
caught. Although they have no power of movement, they are probably of
some use by absorbing animal matter from any minute insect which may be
caught by them, and by absorbing ammonia from the rain-water. But their
varying presence and size, and their irregular position, indicate that
they are not of much service, and that they are tending towards
abortion. In a future chapter we shall see that Drosophyllum, with its
elongated leaves, probably represents the condition of an early
progenitor of the genus Drosera; and none of the tentacles of
Drosophyllum, neither those on the upper nor lower surface of the
leaves, are capable of movement when excited, though they capture
numerous insects, which serve as nutriment. Therefore it seems that
Drosera binata has retained remnants of certain ancestral
characters namely a few motionless tentacles on the backs of the
leaves, and fairly well developed sessile glands which have been lost
by most or all of the other species of the genus.]
Concluding Remarks. From what we have now seen, there can be little
doubt that most or probably all the species of Drosera are adapted for
catching insects by nearly the same means. Besides the two Australian
species above described, it is said* that two other species from this
country, namely Drosera pallida and Drosera sulphurea, close their
leaves upon insects with great rapidity: and the same phenomenon is
manifested by an Indian species, D. lunata, and by several of those of
the Cape of Good Hope, especially by D. trinervis. Another Australian
species, Drosera heterophylla (made by Lindley into a distinct genus,
Sondera) is remarkable from its peculiarly shaped leaves, but I know
nothing of its power of catching insects, for I have seen only dried
specimens. The leaves form minute flattened cups, with the footstalks
252