DETERMINATION OF THE LATENT PERIOD 117 



number of spaces before the initiation of response is eight, 

 the latent period being therefore 'oS 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 



Fig. 69. — Record of L of Mimosa with a 200 D.V. recorder. 



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 photo- 

 graphic 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 photo- 

 graphic 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 ^-J ^ part of a second. 

 In other words, the calculation can be carried into 

 thousandths of a second. In the present case there are 



