706 J. P. Nitsch and C. Nitsch 



volume contains a number of recent references to oxygen toxicity, but 

 a fuller appreciation of the phenomenon can be gained by examina- 

 tion of older studies (Clements, Carnegie Inst., \V'^ashington, 1921). The 

 toxic effects of oxygen on plants were known to Scheele (1777), Huber 

 and Senebier (1801), etc. The benefits of reduced (sub-atmospheric) 

 oxygen levels were appreciated by Sedebeck (1881) and Jaccard (1893). 

 We have, on the whole, relegated such nonchemical effects and ob- 

 servations to the physiology of our earlier day, and pursued the study 

 of chemical growth factors without regard to nonmetabolic oxidation. 

 Now we are confronted with observations which suggest that the 

 functions of growth factors be re-examined, keeping in mind the 

 duality of oxygen as part of the biological milieu. 



Dr. Stowe was concerned about the discrepancies in growth rate 

 between sections and intact organs. He sought to narrow the gap, 

 finally by application of unsaturated lipids. Drs. Crosby and Vlitos 

 discovered that fatty substances could supplant conventional auxins 

 as growth factors. Dr. Crosby recognized the antioxidant character of 

 some indolic auxins. Dr. Marre discussed growth inhibitions which 

 he associated with oxidized ascorbic acid, and speculated that ascorbic 

 acid might also be a growth promoter (but only, we suggest, in re- 

 duced form). Dr. van Overbeek alluded to the importance of acid 

 and the reducing environment of archeozoic times but did not dis- 

 tinguish between oxygen uptake, respiration, and energetic processes, 

 thus leaving the issue unsettled. Drs. Muir and Hansch, and Dr. 

 Thimann considered the electronic features of organic compounds as 

 directly related to their auxin or auxin-like properties. From their 

 comments we would assume that electron delocalization, polarization, 

 and local electron densities are important in relation to attachment of 

 the hormone to its acceptor. Now, the significance of electrical forces 

 in the localization of hormones is obvious, but it was somewhat sur- 

 prising that those who treated these matters wuth such facility did not 

 carry their consideration of electron mobility beyond the primary 

 events of auxin-acceptor interaction. 



The true mechanism of action of auxin or other growth factors 

 is hardly to be found in a consideration of attachment, nor in delibera- 

 tions on the biophysics of the cell wall. Thus, a knowledge of the 

 factors which enable auxin to be delivered to the right place in the 

 cell still leaves unanswered the question: "What does the auxin do 

 when it gets there?" No laboratory has yet answered this cjuestion, 

 but we contend that important elements of the answer reside in those 

 electronic properties which are particularly meaningful when con- 

 sidered together with oxygen toxicity. "Antioxidant" and "reducing" 

 are operational terms. They a})ply to molecules, or ions, which are 

 characterized more fundamentally by their high electron availability. 



