1909.] 



Vegetable Assimilation and Resjnration. 



27 



halves of the leaf, and the heavy line to measurements along the midrib. 

 The sky was somewhat cloudy, and periods in which clouds passed over the 

 sun are indicated by shading on the right-hand side, corresponding to the 



3 6769 I0UIZI 



Ante meridianuiiTi. 



.23456 



Post merldianum . 



Fig. 5. — Cur^-es showing temporary expansion of leaves of Helianthus annmis during 

 interval of cloud and rain on July 25, 1908. Ordinates are the percentage excess of 

 the area over that at 5 a.m. on July 22. 



times which are shown on the left. The 5-miuute observations commenced 

 at 10.45, and the changes observed, as bright sunshine alternated with shade, 

 were remarkably rapid. For instance, the left half of the leaf increased 



