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.’ It is interesting in this connection to refer to the response of the leaf of Water Mimosa (_Neptunia oleracea_). Here the reaction is very sluggish in comparison with that of _Mimosa pudica_. A tabular statement of contractile response of various radial, anisotropic and pulvinated organs will show a continuity in the contractile reaction; the difference exhibited is a question of degree and not of kind. TABLE 1--PERIODS OF MAXIMUM CONTRACTION AND OF RECOVERY OF DIFFERENT PLANTS. +-------------------------------------+-------------+------------+ | | Period of | Period of | | Specimen | maximum | recovery. | | | contraction | | +-------------------------------------+-------------+------------+ | Radial organ: | | | | Tendril of _Passiflora_ | 100 seconds | 4 minutes.| | | | | | Anisotropic organ: | | | | Hooked tendril of _Passiflora_ | 120 " | 13 " | | | | | | Pulvinated organ: | | | | Pulvinus of _Neptunia Oleracea_ | 180 " | 57 " | | | | | | Pulvinus of _Mimosa pudica_ | 3 " | 16 " | +-------------------------------------+-------------+------------+