granular matter.* There is, however, a narrow zone close beneath the
glands of the longer tentacles, and a broader zone near their bases, of
a green tint. Spiral vessels, accompanied by simple vascular tissue,
branch off from the vascular bundles in the blade of the leaf, and run
up all the tentacles into the glands.
Several eminent physiologists have discussed the homological nature of
these appendages or tentacles, that is, whether they ought to be
considered as hairs (trichomes) or prolongations of the leaf. Nitschke
has shown that they include all the elements proper to the blade of a
leaf; and the fact of their including vascular tissue was formerly
thought to prove that they were prolongations of the leaf, but it is
now known that vessels sometimes enter true hairs.** The power of
movement which they possess is a strong argument against their being
viewed as hairs. The conclusion which seems to me the most probable
will be given in Chap. XV., namely that they existed primordially as
glandular hairs, or mere epidermic formations, and that their upper
part should still be so considered; but that their lower
* According to Nitschke ( Bot. Zeitung, 1861, p. 224) the purple fluid
results from the metamorphosis of chlorophyll. Mr. Sorby examined the
colouring matter with the spectroscope, and informs me that it consists
of the commonest species of erythrophyll, which is often met with in
leaves with low vitality, and in parts, like the petioles, which carry
on leaf-functions in a very imperfect manner. All that can be said,
therefore, is that the hairs (or tentacles) are coloured like parts of
a leaf which do not fulfil their proper office.
** Dr. Nitschke has discussed this subject in Bot. Zeitung, 1861, p.
241 &c. See also Dr. Warming ( Sur la Diffrence entre les Trichomes
&c., 1873), who gives references to various publications. See also
Groenland and Trcul Annal. des Sc. nat. bot. (4th series), tom. iii.
1855, pp. 297 and 303. [page 6]
part, which alone is capable of movement, consists of a prolongation of
the leaf; the spiral vessels being extended from this to the uppermost
part. We shall hereafter see that the terminal tentacles of the divided
leaves of Roridula are still in an intermediate condition.
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