Page:Researches on Irritability of Plants.djvu/100

Rh same improvement of tone might take the form of a gradually increasing excitability. Hence the gradual bettering the tonic condition, under successive stimulations, may often find two simultaneous expressions. In the first place the growing tone, with its increasing normal tonic contraction, will be seen in the shifting of the base-line upwards. Secondly, it will be exhibited in the growing amplitude of successive responses. These two features will

both be noticed in the record depicted in fig. 38. Here, as might be expected, in a specimen in sub-tonic condition we find that the first stimulus gives rise to a relatively feeble response. But in consequence of stimulation the tonic condition itself is improved, as demonstrated by the fact that the leaf remains in a slightly more contracted attitude than at the beginning. The next stimulus finds it in a better tonic condition, with accompanying higher excitability. Hence the response is larger. In this way the tonic