FORMATION AND OCCURRENCE OF AUXINS 65 



seeded plants, which do not show any regeneration, were 

 used. The evidence is therefore strong that a precursor, 

 present in the seed, moves up into the coleoptile tip and is 

 there converted into auxin. Some of it is doubtless also 

 converted into auxin in the seed itself. 



It will be seen that few general conclusions can be drawn 

 as to auxin production during the early seedling stages. 

 Ungerminated seeds certainly contain some auxin, but the 

 amounts found are extremely variable, partly due to diffi- 

 culties of extraction, and partly due to variation in the ex- 

 tent of wetting, which according to Cholodny (1935) causes 

 rapid auxin formation. 



This rapid formation of free auxin is presumably from 

 the precursor. It may be suggested that this precursor is an 

 ester, the esters of auxin a being themselves inactive. This 

 would explain the results of Pohl (1936), who found that if 

 Avena seeds were cut open and electrolyzed (c/. p. 63), the 

 subsequent growth of the coleoptile was reduced. If now the 

 electrolyzed seeds were soaked in a solution of auxin a the 

 subsequent growth of the coleoptile was more nearly normal, 

 but soaking in a solution of indole-acetic acid did not have 

 this effect. The auxin a, if the above \'iew is correct, would 

 be esterified and the ester carried to the tip of the young 

 coleoptile. The esters of indole-acetic acid, being readily 

 hydrolyzed in the plant (cf. VII E) could not be so trans- 

 ported on account of the polarity of the coleoptile. This 

 suggestion is also supported by the work of Kogl, Erxleben, 

 and Haagen Smit (1934), who obtained considerable yields 

 of auxin after the saponification of various oils prepared 

 from seeds. 



As to the auxin in the seedling, probably much of the 

 variation between the results of different authors is due to 

 inactivation during the extraction (see below). In general, 

 the production of auxin takes place in the apical parts of all 

 organs which are actively elongating, such as terminal buds 



cause no curvatures within the first three hours but then produce definite negative 

 curvatures. 



