1904] DARWIN; MOVEMENTS OF STOMATA 105 
only evidence of periodicity which I have obtained. It corre- 
sponds exactly to some of Pfeffer’s experiments on the “sleep” 
of flowers.%3 On the other hand, my curves do not confirm the 
more detailed differences between the behavior of the stomata 
in the morning and afternoon, as given in my Obdservations at 
the foot of p.596. This is a difficulty which I hope to clear up. 
BOTANICAL LABORATORY, 
Cambridge, England. 
*3 Physiol. Untersuchungen. 1873. 
