I. W. BAILEY 



521 



120 YR& 



LENGTH -MILLIMETERS 



Text-Fig. 1. Frequency curves showing variation in the size of cambial 

 initials in stems of different ages. 



100 



200 



SOO 



AGE-YEARS 



Text-Fig. 2. A, curve showing variations in the average size of large cambial 

 initials with increasing age o*f a stem. B, size level of cells of the general order 

 of magnitude of the cells of the embryo and growing points. E and E', curves 

 showing effects of experimentally induced changes in cell size. 



