strange fact that Dionaea, which is one of the most beautifully adapted
plants in the vegetable kingdom, should apparently be on the high-road
to extinction. This is all the more strange as the organs of Dionaea
are more highly differentiated than those of Drosera; its filaments
serve exclusively as organs of touch, the lobes for capturing insects,
and the glands, when excited, for secretion as well as for absorption;
whereas with Drosera the glands serve all these purposes, and secrete
without being excited.
By comparing the structure of the leaves, their degree of complication,
and their rudimentary parts in the six genera, we are led to infer that
their common parent form partook of the characters of Drosophyllum,
Roridula, and Byblis. The leaves of this ancient form were almost
certainly linear, perhaps divided, and bore on their upper and lower
surfaces glands which had the power of secreting and absorbing. Some of
these glands were mounted on pedicels, and others were almost sessile;
the latter secreting only when stimulated by the absorption of
nitrogenous matter. In Byblis the glands consist of a single layer of
cells, supported on a unicellular pedicel; in Roridula they have a more
complex structure, and are supported on pedicels formed of several rows
of cells; in Drosophyllum they further include spiral cells, and the
pedicels include a bundle of spiral vessels. But in these three genera
these organs do not possess any power of movement, and there is no
reason to doubt that they are of the nature of hairs or trichomes.
Although in innumerable instances foliar organs move when excited, no
case is known of a trichome having such [page 359] power.* We are thus
led to inquire how the so-called tentacles of Drosera, which are
manifestly of the same general nature as the glandular hairs of the
above three genera, could have acquired the power of moving. Many
botanists maintain that these tentacles consist of prolongations of the
leaf, because they include vascular tissue, but this can no longer be
considered as a trustworthy distinction.** The possession of the power
of movement on excitement would have been safer evidence. But when we
consider the vast number of the tentacles on both surfaces of the
leaves of Drosophyllum, and on the upper surface of the leaves of
Drosera, it seems scarcely possible that each tentacle could have
aboriginally existed as a prolongation of the leaf. Roridula, perhaps,
shows us how we may reconcile these difficulties with respect to the
homological nature of the tentacles. The lateral divisions of the
leaves of this plant terminate in long tentacles; and these include
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