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36 insensitive, are also found to exhibit responsive movements.

The most striking and familiar example of response is afforded by the main pulvinus of Mimosa pudica of which a record is given in Fig. 12. It is generally assumed

that sensibility is confined to the lower half of the organ. It will be shown in a subsequent Paper that this is not the case. The upper half of the pulvinus is also sensitive though in a feeble degree, its excitability being about 80 times less than that of the lower half. On diffuse stimulation the predominant contraction of the lower half causes the fall of the leaf, the antagonistic reaction of the upper half being, in practice, negligible. In order to avoid unnecessary repetition, I shall ignore the feeble antagonistic reaction of the less excitable half of the organ, and shall use the word 'contraction' for 'relatively greater contraction.'