Page:Researches on Irritability of Plants.djvu/140

Rh number of spaces before the initiation of response is eight, the latent period being therefore .08 second. The closeness of the time-dots is not any great difficulty here, as with the help of a magnifying glass it is quite easy to make the necessary observation.

For the determination of the latent period in plants this accuracy of an order higher than hundredths of a second is more than ample. But such a limit is easily exceeded. As an example of this, I give a record (fig. 69) made with a different recorder, whose frequency was an octave higher than the last—namely, 200 double vibrations

each second. The successive dots are therefore in this case part of a second apart. It has been said already that by slowing the travel of the recording plate the abruptness of the flexure of the curve would be increased, the spaces between the dots being at the same time shortened. But we may obtain wider spacings without losing this sharpness of flexure, by making a magnified photographic reproduction of the curve, as shown in the next figure (fig. 70), which is a reproduction of the first part of the record in fig. 69 enlarged about three times by photographic means. In this way it is not difficult to measure, say, one-fifth of the distance between two successive dots, themselves representing an interval of $1⁄200$ part of a second. In other words, the calculation can be carried into thousandths of a second. In the present case there are