ROBERT M. MUIR 



363 



Wildman (4) have pointed out, the acid-alkah destruction test is in- 

 conclusive because of the interference by proteins and inhibitors. The 

 possibihty that different auxin types occur in the pollen and ovary 

 tissue merits further investigation. 



Remaining to be investigated are many other aspects of the mechanism 

 of auxin production in the pistil following fertilization. The greatest 

 need exists for the re-examination of the auxin content of the pollen 

 and pistil of the plants previously studied, this time using uniform tech- 

 niques of auxin analysis to obtain conclusive evidence as to the similarity 

 or dissimilarity of the mechanism in different species. In the pistil of 



TABLE 5 

 Auxin yields from 30 mg. pollen following hydrolysis 



Nicotiana tabacum, and perhaps other species also, following fertihzation, 

 a system for the production of diffusible, free auxin is established. The 

 auxin production parallels the enlargement of the fruit, greatly exceeding 

 the amount of auxin present in the pollen. The auxin in the ovary may 

 be formed from tryptophan or a similar precursor, the pollen furnishing 

 a part of a system responsible for the production of tryptophan in the 

 tissues; or the auxin may be formed from other precursors, perhaps 

 protein in nature, a substance in the pollen bringing about the release of 

 the auxin from its inactive combination. The activator or coenzyme 

 nature of the effective substance in pollen remains to be established. 



