8 BOTANICAL GAZETTE [JULY 
is formed. This process is repeated indefinitely. The rapidity of 
succession of zones is dependent solely upon the relation which rapidity 
of branching bears to rapidity of increase in length. Slow lineal 
1G. 6.—A scochyta Chrysanthemi Stevens; plate culture showing that the forma- 
tion of zones is not coincident with diurnal changes; ink marks show growth for three 
consecutive days. 
Fic. 7.—Diagram showing, at right, the zones (stippled) and diurnal marks; at 
left, theoretical expression of cause of zonation 
