_Response of Zephyranthes: Experiment 113._--Viewed from the top, the inner side of the petal of a flower is the upper side. The _Crocus_ flower under rise of temperature opens outwards by expansion of the inner side, which must be the more excitable. As _Crocus_ was not available in Calcutta, I found the flower of _Zephyranthes_ (sometimes called the Indian _Crocus_) reacting to variation of temperature in a manner similar to that of _Crocus_, that is to say, the flower opens under rise and closes with a fall of temperature. For obtaining record all the perianth segments but one was removed. This segment was attached to the recording lever. On lowering of temperature through 5°C. there was an up-movement, or a movement of closure. Rise of temperature induced, on the other hand, a movement of opening. [Illustration: FIG. 109.--Thermonastic and radionastic responses of petal of _Zephyranthes_ C, closing movement due to cooling, and H, opening movement due to warming; R, closing movement due to heat-radiation. Note opposite responses to rise of temperature and to thermal radiation.] _Effect of thermal radiation: Experiment 114._--I stated that the effect of thermal radiation acts as a stimulus, inducing a reaction which is antagonistic to that of rise of temperature. In verification of this, I subjected the specimen to the action of infra-red radiation acting from all sides. The result is seen in the responsive movement of closure (Fig. 109 R). These experiments demonstrate clearly that the responses to rise of temperature and thermal radiation are of opposite signs. As a movement of closure was induced by the diffuse stimulus of thermal radiation, it is evident that this must have been brought about by the greater contraction of the inner half of the perianth; hence the inner half of the organ is relatively the more excitable. [Illustration: FIG. 110.--The Thermonastic Recorder. T, metallic thermometer attached to the short arm of the upper lever; the specimen of _Nymphæa_, N, has one of its perianth leaves attached to the short arm of the second lever by a thread. C, clockwork for oscillation of the plate.] NEGATIVE THERMONASTIC RESPONSE. _Response of_ Nymphæa: _Experiment 115._--Many of the Indian _Nymphæaceæ_ have their sepals and petals closed during the day, and open at night. I find that the perianth leaves of this flower are markedly sensitive to variation of temperature. The Thermonastic Recorder employed in this investigation is shown in figure 110. The record given in figure 111 shows that the perianth segment, subjected to a few degrees' rise of temperature, responded by an up-movement of closure, due to greater expansion of the outer half. The latent period was 6 seconds, and the maximum effect was attained in the further course of 21 seconds. This experiment shows that the thermonastic response of this flower is of the negative type.