Investigation of natural auxins and growth inhibitors 



relatively well to added lAA. In oiu- experiments, the coleoptiles were 

 sectioned when they had reached about 25 mm in length and the internodes 

 about 20 mm. 



If one wants to employ small volumes of test solutions, it is important to 

 wash the sections before use. The length and the nature of this pretreatment 

 was investigated. It was found that washing both coleoptiles and mesocotyls 

 for one hour in glass-distilled water increased the lAA response and the 

 reproducibility of the test results ( Table 6) . If the presoaking time is increased, 

 the response to lAA decreases. It also decreases if the sections are immersed. 



Table 6 



Effect of various pretreatments on the response to lAA 



Ten 4 mm sections were used in each case. The sections were ahvays breaking the surface 

 of the sohitions unless otherwise indicated. 



t Immersion in water increases somewhat the length of the controls, but a close examination shows that the 

 sections become more slender than when they are floated. 



This decrease, however, can be prevented by the addition of sucrose (2 per 

 cent). Immersion in the liquid presents no problem for coleoptiles which 

 naturally float on the solutions, but, in the case of first internodes which are 

 of solid stem tissue, it was necessary to lay them on stretched cheese-cloth to 

 keep them breaking the surface of the solution. It was thought that the 

 increase in response to lAA caused by presoaking in water might be due to 

 the washing away of an lAA-destroying system. To test this idea, presoaking 

 in reducing agents such as ascorbic acid, glutathione, Na2S204 was tried, 

 but with no significant results. Nor did presoaking in Ca pantothenate, 

 folic acid, arginine, or cobalt chloride (10-1,000 y/1) have any appreciable 

 effect. On the contrary, manganese, which is well known to stimulate 

 growth when used together with lAA, was found to increase the growth of 

 coleoptiles but not of internodes when supplied in the pretreatment water at 

 the concentration of 5-9 X 10~^ M. However, we did not add MnS04 to the 

 solutions during the whole test period for fear that it might help to destroy 

 labile substances present in the plant extracts. In summary, a 3-hour 



19 



