An inspection of the record given in Fig. 29 shows that the amplitude of response was enhanced after 4 P.M. The temperature up to that time was unusually high (38°C.), and there was in consequence a depression of excitability. After that hour there was a mitigation of heat, the temperature returning towards the optimum. Hence we find that the maximum excitability was attained between the hours 4 and 6 P.M. The minimum temperature at night was higher in the present case than that of the experiment carried out in February; in the former the minimum was 25.5°C., while in the latter it was 19.5°C. On account of this difference the night record in summer shows a fall of excitability which is far more gradual than that obtained in spring. The excitability is here not totally abolished in the morning, but reaches a minimum after 8 A.M.; the sensitiveness is then gradually enhanced in a staircase manner. TABLE III--SHOWING THE RELATION BETWEEN HOURS OF THE DAY, TEMPERATURE, AND EXCITABILITY. (SUMMER SPECIMEN.) +--------------------------------+--------------------------------+ | _Hours _Tempera- _Amplitude | _Hours _Tempera- _Amplitude | | of ture._ of | of ture._ of | | day._ Response._ | day._ Response._ | +--------------------------------+--------------------------------+ | 1 p.m. 38° C. 22 mm | 1 a.m. 26° C. 21.5 mm. | | 2 " 38° " 23 " | 2 " 26° " 20 " | | 3 " 38° " 24.5 " | 3 " 25.5° " 18.5 " | | 4 " 37° " 28 " | 4 " 25.5° " 17 " | | 5 " 35.5° " 29 " | 5 " 25.5° " 16 " | | 6 " 33° " 27 " | 6 " 26° " 15 " | | 7 " 31° " 26 " | 7 " 27° " 14 " | | 8 " 30° " 26 " | 8 " 29° " 13 " | | 9 " 29° " 25 " | 9 " 30.5° " 11 " | |10 " 27° " 24.5 " |10 " 33° " 16 " | |11 " 27° " 24 " |11 " 35° " 17 " | |12 " 26.5° " 22.5 " |12 " 37° " 21 " | +--------------------------------+--------------------------------+ SUMMARY. The moto-excitability of _Mimosa_ was gauged every hour of the day and night, by the amplitude of the response to a testing stimulus. This is effected by means of automatic devices which excite the plant periodically by an absolutely constant stimulus, and record the corresponding mechanical response.