Plant Qrowth'Suhstances 



of the growth-promoting value of extracts from rotted organic 

 matter were sound. 



In view of this, it seems desirable to restore the term 

 "auximone", which is historically valid. It should be remem- 

 bered that growth-regulation and growth-promoting are 

 not synonymous. If "auximone" is thought not to be logical 

 (Greek auximos : promoting growth) there would seem to be 

 no alternative to the generic use of either "phytamin" or 

 growth-regulating substance: the latter may, however, be 

 shortened to growth-substance. 



The term growth-substance, or growth-regulating sub- 

 stance in the current sense as applied to plants, was intro- 

 duced by R. Snow about 1928.^ It is admittedly not free from 

 objection, being vague (Avery (1937) ) but, if used in con- 

 junction with the adjective "synthetic", expressed or under- 

 stood, it at least avoids confusion with hormonal substances. 

 These also are, of course, growth-substances or -factors, but, 

 being hormones, such can be definitely named as a class. We 

 thus have the division of all plant-growth substances into : 



(i) Hormones (phytohormones) : 



(a) auxins (auxin-a, auxin-b). 



(b) vitamins (B^, C, . . .) 



(c) rhizocaline, florigen, . . . 



(2) Synthetic growth-substances (drugs). 



This classification is not ideal, for it suffers from the classifi- 

 catory disadvantage that vitamin C is a true hormone in the 

 plant, but when applied as a drug it enters division (2), 

 producing as a drug a possibly different effect from that which 

 it brings about hormonally. 



Division (2) might be divided in terms of Went's biphasic 

 actions, but his name sub-auxin for e.^., phenyl-butyricacid, 

 does not seem logical, as that substance is not an auxin or 

 chemically auxin-like, and is not a hormone. 



The term "auxin" for the whole class of growth-substances 



^The acknowledgment given to Dr. T. Eden in the first edition was meant 

 to thank him for bringing this term to the author's notice — not that Eden has 

 introduced the term into general use. It is regretted that this was not made 

 clear. 



96 



