Page:Insectivorous Plants, Darwin, 1899.djvu/24

{|width=100%
 * align="left"|4
 * align="center"|DROSERA ROTUNDIFOLIA.
 * align="right"|[Chap. I.
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The tentacles on the central part of the leaf or disc are short and stand upright, and their pedicels are green. Towards the margin they become longer and longer and more inclined outwards, with their pedicels of a purple colour. Those on the extreme margin project in the same plane with the leaf, or more commonly (see Fig 2.) are considerably reflexed. A few tentacles spring from the base of the footstalk or petiole, and these are the longest of all,

(Drosera rotundifolia.) Old leaf viewed laterally ; enlarged about five times.

being sometimes nearly ¼ of an inch in length. On a leaf bearing altogether 252 tentacles, the short ones on the disc, having green pedicels, were in number to the longer submarginal and marginal tentacles, having purple pedicels, as nine to sixteen.

A tentacle consists of a thin, straight, hair-like pedicel, carrying a gland on the summit. The pedicel is somewhat flattened, and is formed of several rows of elongated cells, filled with purple fluid or 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 fonnerly thought to prove that they were prolongations of the leaf, but it is now known that vessels sometimes enter true hairs.