148 PHOTOCONTROL OF GROWTH 



by 150 mm test tube. They were then covered with boihng distilled 

 water and boiled in a water bath on a hot plate for 20 min. The fluid 

 was decanted, and adjusted to such a volume that each milliliter repre- 

 sented 10 mg fr. wt. of the original plant material. Two-tenths milH- 

 liter (equivalent to 2 mg fr. wt.) of this inhibitor extract was then 

 added per the usual 10 ml of reaction mixture. Results of such in- 

 hibitor assays are shown in Table IV. 



Table IV. Comparative lAA Oxidase Inhibitor Content of Youngest Expanded 

 Leaflets of 14-Day-Old Dwarf (Laurel) and Tall (Alaska) Pea Seedlings. (Inhibitor 

 extracted by direct boiling in distilled water, of the intact leaflet. The equivalent of 

 2 mg fr. wt. of leaflet was then added as hot aqueous extract per 10 ml of usual 

 reaction mixture. Original Salkowski color = 270.) 



It is clear that Alaska (tall) leaflets have about three times as much 

 inhibitor as Laurel (dwarf) leaflets per unit fresh weight. This is con- 

 sistent with the view that inhibitor controls growth by sparing auxin 

 from destruction. Similar assays of terminal buds, young stem and old 

 stem showed smaller differences, but always in the same direction. In 

 view of the fact that the youngest expanded leaflets are richest in the 

 inhibitor, data obtained from these organs are considered the more 

 significant. 



Effect of Gibberellic Acid Pretreatment on lAA Oxidase Inhibitor 

 in Leaflets of Alaska and Laurel Peas. It has been shown for peas 



