MEMOIRS OF THE NEW YORK BOTANICAL GARDEN. 167 



lOnun-- 



10 



mm- 



lOnun-- 



10 



mm-- 



10 



mm.- 



6 8 10 12 



P.M. 



Fig. 128. Curve of growth of etiolated petiole of Rheum in dark chamber at tem- 

 peratures 2i-23°C. The actual amount of growth during the two hour periods is denoted 

 bj half the distance from the base line at a point above the numerals to the wavy line 

 denoting rate of growth. 



