614 



A. W. Galston and D. C. McCune 



to 100 mm. long epicotyls, yields below additive growth increments in 

 the presence of lAA. Thus, it is clear that in no instance is there 

 any GA-IAA synergism. This disagrees with some of our previous re- 

 sults (7) for reasons which we cannot at present explain. Drs. ^V. S. 

 Hillman and \\\ K. Purves have also obtained data like those in 

 Table 1, and pointed out the non-synergistic interaction to us. Their 

 results will be published elsewhere. 



Similar experiments were performed with stem sections derived 

 from green peas grown under 8, 16.5, and 24 hr. daily light periods. 

 The results are shown in Table 2, from which the following conclu- 

 sions can be drawn: (a) Endogenous growth and response to exogenous 

 lAA are lower in sections derived from the 8-hr. photoperiod plants 

 than in those from 16 and 24 hr. plants, (b) GA response is independ- 

 ent of the photoperiod of the parent plant and is markedly lower 

 in green tissue than in etiolated tissue. Although GA response in the 



Table 2. GA-IAA synergism in green pea stem sections as affected by daily dura- 

 tion of light to which the parent plant was exposed. Details as in Table 1 . 



absence of lAA is small, it is not completely lacking as in the ex- 

 periments of Brian and Hemming (2). (c) Marked GA-IAA synergism 

 occurs in the 8 hr. sections, none in the other sections. 



An experiment was next performed to study the effect of passage 

 of GA through various lengths of green stem tissue on its subsequent 

 interaction with lAA administered to sections excised from the pre- 

 treated stems. Previous experiments had reported such effects to be 

 large (8). For this purpose, green plants were harvested from the 8, 

 16.5, and 24 hr. photoperiod rooms, decapitated just below the ter- 

 minal bud, cut to lengths of 20, 50, or 100 mm., and then freed of all 

 leaves. These leafless stems were then immersed basally in GA (10-* 

 M -|- 1 per cent sucrose -f buffer) or control solutions for 1 hr. After 

 this, apical sections were excised, placed in lAA-containing (or 

 control) solutions, and permitted to grow for 18 hrs. The results 

 are shown in Table 3. It can be seen that in all three groups there 

 was a synergism manifested in the 100 mm. lengths, while only the 

 8 hr. group showed synergism at the 20 mm. length (and in the 5 



