_Experiment 209._--One of the perianth leaves was attached to one of the recording levers, the differential thermometer being attached to the other. It will be seen (Fig. 198) that the movement of the flower follows very closely the curve of variation of temperature. The flower was tightly closed in the day time; and the perianth leaves began to open out in the evening at first slowly, then very rapidly, and the flower becoming fully expanded by 10 p.m. at night. Though the temperature continued to fall, there was no possibility of further expansion beyond the maximum. The temperature began to rise after passing through the minimum at 6 a.m., and the movement of closure set in with rising temperature, the flower becoming completely closed by 10 a.m. That geotropism has little effect is seen from the fact that the inversion of flower does not interfere with the normal opening or closing of the flower. The phenomenon of diurnal movement of _Nymphæa_ is therefore thermonastic, the floral leaves exhibiting movement of opening at night owing to fall of temperature. _Luffa acutangula_, which opens in the afternoon, and closes early in the morning, gives a diurnal record similar to that of _Nymphæa_. SUMMARY. The flower of _Nymphæa_ exhibits a movement of closure during rise of temperature, and of opening during fall of temperature. It is shown further that the effects of light and of rise of temperature are antagonistic to each other. Light is shown to induce in _Nymphæa_ the movement of opening, and darkness to cause the movement of closure. The diurnal movement of _Nymphæa_ is not therefore due to periodic variation of light and darkness, but to the predominant effect of variation of temperature. The diurnal record shows that the perianth leaves begin to open in the evening with falling temperature, and the flower becomes fully expanded by 10 p.m. The movement of closure sets in with rising temperature in the morning, and the flower becomes fully closed by 10 a.m. XLIX.--DAILY MOVEMENT IN PLANTS DUE TO THERMO-GEOTROPISM _By_ SIR J. C. BOSE, _Assisted by_ LALIT MOHAN MUKHERJI. Of the vast number of daily movements perhaps the largest proportion is due to thermo-geotropic reaction and its modifications. Thermo-geotropic movements have the following characteristics: 1. The organs are sensitive to the stimulus of gravity and the periodic movements are brought about by variation of geotropic curvature under change of temperature. 2. The movement is not confined to growing organs, but is also exhibited by organs which are fully grown and even by rigid trees. 3. The periodic movement is closely related to the diurnal variation of temperature. Fall of temperature from thermal-noon (about 2 p.m.) to thermal-dawn (about 6 a.m.) is attended by a movement of erection; rise of temperature from thermal-dawn to thermal-noon is followed, on the other hand, by a reverse movement of fall.