Characteristics of an Inhibitor From Woody Shoots 135 



on detached half nodes in a humid chamber (10), either treated with 

 various concentrations of a-naphthaleneacetic acid or not. Some tests 

 on bean explants^ similarly showed no definite effect of the inhibitor. 



Respiiation of Coleoptile Sections 



No differences could be detected either in oxygen uptake or car- 

 bon dioxide output after tipping inhibitor into the Warburg flasks, 

 although growth was greatly reduced; the sections were in K2HPO4 

 buffer at pH 4.6 at 20° C. This inhibitor evidently does not affect 

 growth by a general reduction in metabolic activity. 



Permeability of Cells to Water 



The short-term effect of inhibitor on water exchange, which was 

 independent of growth, was studied by observing the rate of loss of 

 fresh weight by potato discs in 0.5 M mannitol solution with or with- 

 out inhibitor at 10 ints/ml, and the rate of recovery of plasmolyzed 

 discs on their return to water with or without inhibitor. In the 

 former case a loss of 32 per cent of the initial weight, and in the lat- 

 ter a regain of 29 per cent, were unaffected by the presence of inhib- 

 itor, indicating that the inhibitor does not operate by altering the 

 permeability of the protoplast to water. 



Transport of NalAA and Inhibitor Through Coleoptile Sections 



Agar plates 12 X 9 X 1 mm. were prepared containing NalAA at 

 0.25 p. p.m., inhibitor at 10 ints/ml, both, or neither. Coleoptile sec- 

 tions 1 cm. long were cut, and stored on a klinostat at 3° C; at 

 appropriate times samples were taken, the leaf removed, and three 

 sections of 2 mm. cut from the middle region of each 1 cm. section. 

 Three sets of three of these rings were placed lower ends downward 

 onto an agar plate on a glass slide, and a second plate applied on top 

 of the rings; this upper plate was covered by a thin sheet of polyethy- 

 lene, and the whole system stored under humid conditions at 20° C. 

 for times varying from 2 to 23 hrs. Either the upper or the lower plate 

 was a "donor," containing the substance to be transported, and the op- 

 posite one a "receptor" of plain agar; at the end of the period the 

 plates ^\ere separated, cut into three strips, and placed in the stand- 

 ard section test vials w^ith 0.25 ml. water for testing with five coleop- 

 tile sections as usual. The rings used for transport w^ere fixed, and 

 subsequently measured under the microscope. 



Figure 5 shows the response of sections to the material present in 

 donor or receptor plates after periods of transport of 0, 2, 4, 8, 15, or 

 23 hrs. The apical plate is shown on the left of each pair of histo- 

 grams; the donor plate is shaded and the receptor plain. It is clear 

 that the XalAA has behaved "classically," the donor plate in row 



^Kindlv carried out for us by Dr. D. J. Osborne at Oxford. 



