Grassy stalks

Usage examples of pedicels.

Besides the glands, both surfaces of the leaves and the pedicels of the tentacles bear numerous minute papillae, which absorb carbonate of ammonia, an infusion of raw meat, metallic salts, and probably many other substances, but the absorption of matter by these papillae never induces inflection.

In old leaves, however, especially in those which have been several times in action, the protoplasm in the uppermost cells of the pedicels remains in a permanently more or less aggregated condition.

That the contents of the cells of the glands, and afterwards those of the pedicels, are affected in a plainly visible manner by the pressure of minute particles, we shall have abundant evidence when we treat of the aggregation of protoplasm.

If the tentacles of a young, yet fully matured leaf, that has never been excited or become inflected, be examined, the cells forming the pedicels are seen to be filled with homogeneous, purple fluid.

It can be observed much more distinctly in the upper cells of the pedicels than within the glands, as these are somewhat opaque.

Although the leaves at a hasty glance do not appear green, owing to the purple colour of the tentacles, yet the upper and lower surfaces of the blade, the pedicels of the central tentacles, and the petioles contain chlorophyll, so that, no doubt, the plant obtains and assimilates carbonic acid from the air.

Glands and summits of the tentacles alone sensitive--Transmission of the motor impulse down the pedicels of the tentacles, and across the blade of the leaf--Aggregation of the protoplasm, a reflex action--First discharge of the motor impulse sudden--Direction of the movements of the tentacles--Motor impulse transmitted through the cellular tissue--Mechanism of the movements--Nature of the motor impulse--Reexpansion of the tentacles.

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.

I tried this experiment repeatedly, as I was much surprised at the fact, for all other parts of the pedicels are insensible to any stimulus.

In several cases the process travelled down the pedicels for a length twice or thrice as great as that of the glands, in about 10 m.

In the lower part of the pedicels, the action proceeded slower, so that it took about 20 m.

It is an important fact that when an organic or inorganic object is placed on the glands of the disc, and the exterior tentacles are thus caused to bend inwards, not only is the secretion from the glands of the latter increased in quantity and rendered acid, but the contents of the cells of their pedicels become aggregated.

After a short time the glands, thus indirectly excited, transmit or reflect some influence down their own pedicels, inducing aggregation in cell beneath cell to their bases.

It seems at first sight a probable view that aggregation is due to the glands being excited to secrete more copiously, so that sufficient fluid is not left in their cells, and in the cells of the pedicels, to hold the protoplasm in solution.

Some bits of meat, after being left for a considerable time on the pedicels, were pushed upwards, so as just to touch the glands, and in a minute the tentacles began to bend.