_Experiment 94._--In order to show the striking similarity between the response of ‘sensitive’ _Mimosa_ and that of a growing organ, I give a record (Fig. 88) obtained with a growing bud of _Crinum_ under the stimulus of electric shock above the critical intensity. The recorder gave a magnification of a thousand times. In Fig. 88, the normal growth elongation is represented as a down-curve. On the application of stimulus the normal expansion was suddenly reversed to excitatory contraction, the latent period of reaction was one second and the period of the attainment of maximum contraction (apex-time) was 4 minutes. The organ recovered its original length after a further period of seven minutes and then continued its natural growth elongation. Repetition of stimuli gave rise to successive contractile responses which are in every way similar to the mechanical responses of _Mimosa pudica_. The essential similarity of response of pulvinated and growing organs will be seen in the following tabular statement: TABLE XXI.--TIME RELATIONS OF MECHANICAL RESPONSE OF PULVINATED AND GROWING ORGANS. +-------------------------+----------+------------+--------------+ | | Latent | Apex-time. | Period | | Specimen. | period. | | of recovery. | +-------------------------+----------+------------+--------------+ |Motile pulvinus of | | | | | _Mimosa pudica_. | 0.1 sec. | 3 secs. | 16 minutes. | |Motile pulvinus of | | | | | _Neptunia oleracea_. | 0.6 " | 180 " | 60 " | |Growing bud of _Crinum_. | 1.0 " | 240 " | 7 " | +-------------------------+----------+------------+--------------+ The contraction in growing organs under stimulus is sometimes considerable. Thus in the filamentous corona of _Passiflora quadrangularis_ the contraction may be as much as 15 per cent. of the original length. This is not very different from the excitatory reaction of the typically sensitive stamens of the _Cynereæ_, which exhibits a contraction from 8 to 22 per cent. MODIFICATION OF RESPONSE BY CONDITION OF SUB-TONICITY. In _Mimosa_ the normal response to direct stimulus is _negative_, the leaf undergoing a fall. But sub-tonic specimens exhibit a _positive_ response with erection of the leaf. The action of the stimulus itself improves the tonic condition, and the abnormal positive is thus converted into normal negative, through diphasic response (p. 147). Similarly in growing organs, while the normal effect of stimulus is incipient contraction and retardation of growth under condition of sub-tonicity the response is by acceleration of growth. Continuous stimulation converts this abnormal acceleration into normal retardation of growth (p. 225). EFFECTS OF DIRECT AND INDIRECT STIMULUS.