A. ]V. GALSrON AND RAVINDAR KAUR 693 



TABLE 3 



Effect of the Length of the Youngest Internode on the Growth of Pea Stem 



Sections INCUB.^TED in the Presence of Indole Acetic Acid (IAA) and 



GiBBERELLIC AciD (GA). CONCENTRATIONS AS IN TaBLE 2 



Effect of age of plant and of inteyval between harvest and section- 

 cutting on growth. Occasionally, eight- or nine-day-old etiolated peas 

 had to be substituted for seven-day-old peas, and older green peas 

 for the standard 14-day-old peas. Numerous experiments revealed 

 that, so long as the morphology of the terminal portion of the plant 

 was kept reasonably constant, age of the plant was not an important 

 determinant of section growth. Age substitutions were therefore made, 

 but only when necessary. Similarly, within the usual time limits of an 

 experiment, the duration of the interval between harvest and section- 

 cutting had no effect on the growth patterns. 



B. Differential Growth Responses 



Sucrose optimum. Careful studies by Purves (15) have confirmed 

 the report (8) that sucrose promotes the growth of etiolated sections, 

 and that the optimal concentration for growth is ca. 2 per cent. Fig. 

 5 demonstrates that the sucrose optimum for the growth of green 

 sections is 1% in the light and 2-3% in the dark. As previously 

 demonstrated (2, 7) , optimal growth in the light exceeds optimal 

 growth in the dark, indicating the existence of some non-photosyn- 

 thetic photochemical process promoting growth in green sections. 



Indole acetic acid (IAA) optimum. In confirmation of previous 

 reports (8, 18), the IAA optimum for increase in length of etiolated 

 sections of various initial lengths was found to be ca. 10-^ M, and 

 for increase in fresh weight ca. 10-^ M (Figs. 6 and 7) . In contrast, 

 green sections show no optimum at all in the light, growth in length 

 increasing with increasing IAA concentration beyond 3 X 10-* M 

 (Fig. 8) . In the dark, there appears to be a shallow optimum at ca. 



