136 Barlow, Hancock, ajid Lacey 



I losing promoter and the receptor gaining it \vith increasing time of 

 transport; in row 2, with the donor plate at the base of the section, 

 there has been no movement of promoter. Inhibitor has not moved 

 either way (rows 3 and 4), nor has it prevented the basipetal move- 

 ment of promoter; with the mixture of auxin and inhibitor giving 

 a response about the same as the controls to begin with, when applied 

 apically (row 5) the promoter moves out of the donor block, so that 

 it becomes more and more inhibitory, and into the receptor block 

 which becomes more and more promoting. Basal application of the 

 mixture allows no movement so that the net effect of the plate re- 

 mains at about the control level. 



It is of great interest, however, that the sections used for transport 

 have responded equally to promoter applied at apex or base, the 

 length of the rings after 23 hrs. transport time being 108.5 per cent 

 and 109.5 per cent, respectively, of the length of rings between plain 

 agar plates; they also responded similarly to apical or basal supplies 

 of inhibitor (90.5 and 90.6 per cent) or the mixture of inhibitor and 

 promoter (94.0 and 94.6 per cent), implying that these substances can 

 enter the coleoptile at either surface, but only the promoter can 

 leave it, and then only from the basal end. 



The entry at either end to produce the expected promotion or 

 inhibition of growth has been demonstrated in another series of ex- 

 periments with 1 cm. coleoptile sections. Short lengths of polyvinyl 

 chloride tubing of a bore slightly larger than a coleoptile were held 

 in two parallel strips of plasticene on 3 inch x 2 inch glass slides so 

 that pairs of ttibes were in line, with their ends 8 mm. apart; a coleop- 

 tile section was held between the tubes with 1 mm. inserted in each. 

 There were ten pairs of tubes per slide, the left-hand row always re- 

 ceiving the apical end of the section; solutions were dispensed into 

 the appropriate tubes from a micrometer syringe, and after loading 

 with coleoptile sections the slides were placed on a klinostat so that 

 the sections rotated horizontally about their long axes (to keep them 

 straight) . Table 3 shows the results of two experiments averaged to- 

 gether, and indicates that inhibitor at either end reduces growth 

 about equally. Because NalAA is rather more effective supplied api- 

 cally than basally (d vs. b, g vs. c) [confirmed by other experiments 

 here, and with other techniques by Housley, Bcntley, and Bickle (7) 

 and Choudhuri (5)], only strictly comparable treatments must be con- 

 sidered, e.g., compared with water, inhibitor at either entl causes a 

 reduction of 8 per cent (e — f , e — h), but in the presence of promo- 

 ter the real effects of inhibitor are represented not by a — c, and a — 

 g. but by the difference between water and inhibitor at a given end, 

 i.e., b — c = 12 per cent for apically supplied inhibitor, and d — g 

 = 13 per cent when supplied basally. 



