DETECTION OF LATENT STIMULUS 473 



to prevent the loss of water from the cylinder by evaporation, 

 a film of oil covers the surface. In this way I obtained 

 the accompanying record of variation of rate of transpiration 

 in a young specimen of Cucurbita, from 3 P.M. to 12 P.M. 

 (fig. 189). It will be noticed that in this case there is an 

 enhancement of transpiration which continues with a single 

 fluctuation till past 11 P.M., after which there is a sudden 

 depression of the rate. 



Continuous photographic record of the diurnal varia- 

 tion of the rateof growth. — I shall first give a photographic 

 record (fig. icpo^taken from a seedling of Oryza sativa, only 



Fig. 190. Continuous Photographic Record of Variation of Rate of 

 Growth in Four Days' Old Seedling of Oryza sativa, from 3 P.M. 

 till 9 a.m., that is during Eighteen Hours 



four days old. The diurnal periodicity has already, it will be 

 seen, become fairly impressed, though it is not yet sufficiently 

 powerful to mask, to any great extent, the subsidiary periodi- 

 cities induced by other factors. The record, it must be 

 remembered, was taken in continuous darkness, being com- 

 menced at 3 P.M., when it was balanced. From this time to 

 9 P.M. there were three pulsations. From 6 till after 8 P.M. 

 there was depression of the average rate of growth, after 

 which it rose somewhat rapidly till 12.30 A.M., exhibiting 

 during that period two groups of two pulsations each. There 

 was now a quick fall for the next half-hour, and after this 



