_Record in the morning: Experiment 22._--The excitability is, as we have seen, nearly abolished about 8 A.M., after which there is a gradual restoration. This gradual enhancement of excitability to a maximum in the course of the forenoon is seen well illustrated in the record below (Fig. 26). [Illustration: FIG. 26. Morning record from 8 A.M. to 12 noon, exhibiting gradual enhancement of excitability.] The record of daily periodicity given in Fig. 23 may be regarded as a typical example. Modifications may, however, be observed which are traceable to individual peculiarities. As an example of this, I give a record (Fig. 27) obtained with a specimen in which nyctitropic movement was very pronounced. The periodic variation of excitability exhibited here is practically the same as shown by other specimens. The interesting variation is in the character of the recovery from stimulus; the leaf was falling from 6 to 9 P.M.; owing to the shifting of the base-line upwards the recovery appears to be incomplete. After 9 P.M. the leaf was erected, at first slowly, then at a very rapid rate. The consequent fall of the base-line late at night is very abrupt; hence there is an apparent over-shooting in the line of recovery. [Illustration: FIG. 27. Record of diurnal variation of excitability; it exhibits marked nyctitropic movement.] EFFECT OF TEMPERATURE ON VARIATION OF EXCITABILITY. So far I have merely described the observed diurnal variation of excitability. We may next inquire whether there is any causal relation between the change of external conditions and the observed variation of excitability. It has been shown that the moto-excitability is greatly influenced by temperature. In order to find in what manner the diurnal variation of excitability was influenced by the daily variation of temperature, I took special care to secure by means of the thermograph a continuous record of temperature variations. The table which follows shows the relation between the hours of the day, temperature, and amplitude of response, in a typical case of diurnal variation of excitability. TABLE II.--SHOWING THE RELATION BETWEEN HOUR OF THE DAY, TEMPERATURE, AND EXCITABILITY. (SPRING SPECIMEN.)