Characteristics of cm Inhibitor From Woody Shoots 



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CONCN. SODIUM INDOLE-3- ACETATE, RRM. 

 Fig. 4. Average curvature per side of slit pea stems in response to NalAA with 

 (broken lines), or without (solid lines), inhibitor at 10 ints/ml. The curve shows 

 the average response from two separate experiments, the individual values being 

 shown as open and closed circles for sections with and without inhibitor resj^ec- 

 tively. The method of measuring the curvature is shown in the insets. 



(15); they were slit to within 1 cm. of the base, washed in running 

 tap water for a few hours, and then dispensed six to a petri dish con- 

 taining 3 ml. solution. After ca. 20 hrs. tracings were made of the 

 segments, and the amount of curvature measured as shown in the 

 inset on Figure 4 (14). The graphs show the steadily increasing in- 

 ward curvature with increasing concentration of NalAA, and an aug- 

 mentation of this effect by inhibitor at 10 ints/ml except at the high- 

 est auxin level used (3 p.p.m.). 



Interpretation of the results of the slit pea stem test is difficult 

 (15), and without further work it is impossible to say whether the 

 inhibitor has had an "auxin-sparing" effect, making each auxin con- 

 centration in effect higher, or has inhibited the inner tissue more 

 than the outer, so resulting in a greater net inward bending for a 

 given elongation of the outer tissues. Straight grotvth of pea stem sec- 

 tions is certainly inhibited, but only a few tests have been performed 

 and comparable data for inner and outer tissues — the critical point 

 in this connection — have not been obtained. 



Pollen-Tube Extension 



The germination of apple pollen was not greatly affected by even 

 quite high concentrations of inhibitor, but the length of the tubes 



