The antagonistic reactions of light and warmth are found not only in growth but also in the rhythmic activity of _Desmodium gyrans_. In the pulsation of _Desmodium_ the contractile effect of light induces a rapid diminution of the diastolic limit of expansion, while the expansive reaction of warmth brings about a marked reduction of the systolic limit in successive pulsations. XXI.--A COMPARISON OF RESPONSES IN GROWING AND NON-GROWING ORGANS _By_ SIR J. C. BOSE, _Assisted by_ GURUPRASANNA DAS. I have in the preceding series of Papers demonstrated the effects of various forms of stimuli on growth. I have also given accounts of numerous reactions which are extraordinarily similar, in growing and non-growing organs. In fact certain characteristic reactions observed in motile pulvinus of _Mimosa_ and other ‘sensitive’ plants led to the discovery of the corresponding phenomena in growing organs. For fully realising the essential similarity of responses given by all plant-organs, growing and non-growing, I shall give here a short review of the striking character of the parallelism. 1. The incipient contraction of a growing organ under stimulus culminates in a marked shortening of the organ. 2. The similarity of contractile responses in growing and pulvinated organs. 3. Similar modification of both under condition of sub-tonicity. 4. The opposite effects of Direct and Indirect stimulus, both in motile and in growing organs. 5. The exhibition by all plant-organs of _negative_ electric response under Direct, and _positive_ electric response under Indirect stimulus. 6. Similar modification of autonomous activity in _Desmodium gyrans_ and in growing organs under parallel conditions. 7. Similar excitatory effects of various stimuli on pulvinated and growing organs. 8. Similar discriminative effects of different rays of light in excitation of motile and growing organs. CONTRACTILE RESPONSE OF GROWING AND NON-GROWING ORGANS. I have shown (page 198) that a growing organ under stimulus, undergoes an incipient contraction as shown in the responsive retardation of its rate of growth; that this retardation increases with the intensity of the incident stimulus till growth becomes arrested. Above this critical intensity the induced contraction causes an actual shortening of the organ. There is no breach of continuity in the increasing contractile reaction, which at various stages appears as a retardation, an arrest of growth or a marked shortening of length of the organ. CONTRACTILE RESPONSE OF PULVINATED AND GROWING ORGANS. [Illustration: FIG. 88.--Contractile response of growing organ under electric shock. Successive dots at intervals of 4″. Vertical lines below represent intervals of one minute. (Magnification 1,000 times.)]