I shall now describe certain modifications in response, which result from the change of season and also from condition of high temperature. Physiological reactions, generally speaking, are much affected by different seasons; thus the seedlings of _Scirpus Kysoor_ exhibit a very rapid rate of growth of 3 mm. per hour in August, but a month later the growth-rate declines to only 1 mm. per hour. I find similar depression of growth with the advance of season in seedlings of _Zea Mays_, where a very rapid fall in growth takes place in the course of a fortnight. The intensity of geotropic responses, both mechanical and electrical, of _Tropæolum_ declines rapidly in the course of a month from February to March (p. 454). The flowers of _Nymphæa_ began to appear by the end of June when the flower stalks exhibited strong geo-electric response. But later in the season, by July and the beginning of August, the response underwent continuous decline, and by the end of August the response was nearly abolished. Much time had to be spent in perfecting the apparatus, and it was not till the beginning of August that the investigations could be properly started; the responsive indications were, however, marked and definite, though relatively feeble compared to those obtained at the beginning of the season. The decline of the geo-electric response was to a certain extent also due to the prevailing high temperature. _Effect of high temperature._--I shall in the next chapter describe experiments which show that geotropic response is diminished under rise of temperature. The specimens employed for localisation of geo-perceptive layer exhibited, as stated before, a decline of geo-electric response with the advance of the season. This may partly be due to unfavourable season, and partly to high temperature. In the middle of the season the responses were extremely feeble on warm days, but on cool mornings they became suddenly enhanced, to decline once more by the middle of the day. I could sometimes succeed in enhancing the sensitiveness by placing the specimen in a cold chamber. It thus appeared that certain internal change unfavourable for geo-perception takes place at high temperatures, and that the sensitive condition could sometimes be restored by artificial cooling. But later in the season, the internal change, whatever it may be, had proceeded too far, and artificial cooling did not restore the sensitiveness of the specimen. What are the physico-chemical concomitants which distinguish insensitive specimens, in which the electric indications had declined almost to the vanishing point? TEST OF INSENSITIVE SPECIMENS. I shall now describe the various physico-chemical concomitants which accompany the condition of relative insensibility. I have found three different tests: the electric, the geotropic, and the microscopic, by which the sensitive could be distinguished from the insensitive condition. The following tests were made on insensitive specimens.