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Show 234 DROSERA ROTUNDIFOLIA. CHAP. X. glands, and only a few of the i1nmediately surrounding short tentacles are inflected; place it on several glands, and many more are acted on; place it on thirty or forty, and all the tentacles, including the extreme marginal ones, beco1ne closely inflected. vV e thus see that the i1npulses proceeding from a number of glands strengthen one another, spread farther, and act on a larger number of tentacles, than the ilnpulse from any single gland. Transmission of the Motor Impulse.-In every case the impulse from a gland has to travel for at least a short distance to the basal part of the tentacle, the upper part and the gland itself being 1nerely carried by the inflection of the lower part. The impulse is thus always transmitted down nearly the whole length of the pedicel. vVhen the central glands are stimulated, and the extreme marginal tentacles beco1ne inflected, the impulse is transmitted across half the diameter of the disc ; and when the glands on one side of the disc are stimulated, the impulse is transmitted across nearly the whole width of the disc. A gland transmits its motor impulse far more easily and quickly down its own tentacle to the bending place than across the disc to neighbouring tentacles. Thus a minute dose of a very weak solution of ammonia, if given to one of the glands of the exterior tentacles, causes it to bend and reach the centre; whereas a large drop of the same solution, given to a score of glands on the disc, will not cause through their combined influence the least inflection of the exterior tentacles. Again, when a bit of meat is placed on the gland of an exterior tentacle, I have seen movement in ten seconds and repeatedly within a minute; but a much large' r bit placed on several glands on the disc does not cause .. CHAP. X. TRANSMISSION OF MOTOR IMPULSE. 235 the exterior tentacles to bend until half an hour or even several hours have elapsed. The motor impulse spreads gradually on all sides from one or more excited glands, so that the tentacles which stand nearest are always first affected. Hence, when the glands in the centre of the disc are excited, the extreme marginal tentacles are the last inflected. But the glands on different parts of the leaf transmit their motor power in a so mew hat different manner. If a bit of meat be placed on the long-headed gland of a marginal tentacle, it quickly transmits an impulse to its own bending . portion; but never, as far as I have observed, to the adjoining tentacles; for these are not affected until the meat has been carried to the central glands, which then radiate forth their conjoint impulse on all sides. On four occasions leaves were prepared by removing some days previously all the glands from the centre, so that these could not be excited by the bits of meat brought to them by the inflection of the marginal tentacles ; and now these marginal tentacles re-expanded after a time without any other tentacle being affected. Other leaves were si1nilarly prepared, and bits of meat were placed on the glands of two tentacles in the third row from the outside, and on the glands of two tentacles in the fifth row. In these four cases the impulse was sent in the first place laterally, that is, in the same concentric row of tentacles, and then towards the centre; but not . centrifugally, or towards the exterior tentacles. In one of these cases only a single tentacle on each side of the one with meat was affected. In the three other cases, from half a dozen to a dozen tentacles, both laterally and towards the centre, were well inflected or sub-inflected. Lastly, in |