698 LIGHT AND LIFE 



TABLE 6 



Effect of the Pretreatment Time of Sections in 10"^ M GA on 



GA-IAA Synergism in Green Pea Stem Sections Derived from 



8-HOUR Photoperiod Plants 



with lAA. In similar experiments with 5 cm sticks, 10 minutes of 

 exposure to GA were found adequate to induce synergism. 



Cobaltous ion. The cobaltous ion is known to enhance markedly 

 the growth of etiolated pea stem sections in the presence of sucrose 

 (1, 14). The optimum concentration of Co++ for this effect is ca. 

 10-4 M. With green pea sections, on the other hand, growth pro- 

 motion by Co++ is very slight, is independent of sucrose, and is mani- 

 fested (when it occurs at all) at ca. 10-^ M (Table 7) . This is the 

 only instance we know in which green sections respond to lower con- 

 centrations of a growth-promoting material than do etiolated sections. 



Substituted urea herbicides. Substituted ureas such as CMU (3-/?- 

 chlorophenyl- 1,1 -dimethyl urea) and fenuron (3-phenyl- 1,1 -dimethyl 

 urea) have been shown to inhibit the growth of and sometimes to 

 kill green plants (3, 4) and to inhibit the Hill reaction (5) and 

 photosynthetic phosphorylation (13). Figs. 10 and 11 show that both 



TABLE 7 



Effect of Cobaltous Chloride on the Growth of Green Pea Stem Sections 



Incubated in the Presence and Absence of Sucrose 



