be expected to give rise to a positive response in a very young leaf or in a leaf which is becoming yellow with age.
The above anticipations have been found verified in the following experiments. In figure 98 is seen the positive response of a very young leaf of Musa; the next figure shows similar positive response given by a
Fig. 97. Normal electromotive response in a vigorous specimen.
Note the transient positive after-effect.
Figs. 98 and 99. Abnormal positive response in a very young and in a very old specimen.
very old leaf. There is an additional factor, to be presently described, which also tends to induce a positive response.
Effect of Increasing Duration of Exposure
The reaction under light, is within limits, proportional to the quantity of light, that is to say, on intensity
