According to varying circumstances, the same blow will evoke responses of different amplitudes. Early in the morning, after the prolonged inactivity of a cold night, we find the plant inclined to be lethargic, and its first answers correspondingly small. But as blow after blow is delivered, this lethargy passes off, and the replies become stronger and stronger. A good way to remove this lethargy quickly, is to give the plant a warm bath. In the heat of the midday, this state of things is reversed. That is to say, after giving vigorous replies the plant becomes fatigued, and its responses grow smaller. This fatigue passes off, however, on allowing it a period of rest. On increasing the intensity of the impinging stimulus, the response also increases. But a limit is attained, beyond which response can no longer be enhanced. Again, just as the pain of a blow persists longer with ourselves, in winter than in summer, so the same holds good of the reaction of the plant also. For instance, in summer it takes _Mimosa_ ten to fifteen minutes to recover from a blow, whereas in winter the same thing would take over half an hour. In all this, you will recognise the similarity between human response and that of the plant. SPONTANEOUS PULSATION In certain tissues, a very curious phenomenon is observed. In man and other animals, there are tissues which beat, as we say, spontaneously. As long as life lasts, so long does the heart continue to pulsate. There is no effect without a cause. How then was it that these pulsations became spontaneous? To this query, no fully satisfactory answer has been forthcoming. We find, however, that similar spontaneous movements are also observable in plant tissues, and by their investigation the secret of automatism in the animal may perhaps be unravelled.