Plant Qroivth'Substances 



coleoptiles were grown retarded their growth in length 

 (Avery and LaRue (1938) ). 



Duhamet (1939) has shown that indole-acetic acid inhibits 

 or accelerates the growth of isolated (excised) roots according 

 to dose, and has brought forward the fact that the substance 

 acts not only on cellular growth, but also on the proliferation 

 of root meristem. This he claims as new. 



The effectiveness of salts, of esters, and of a nitrile as 

 growth-substances shows that the favourable action of the 

 synthetic growth-substances in proper concentration is not 

 due to acid irritation, as has been pretended by a Continental 

 school of plant physiologists. Quantitatively at least, the 

 action of the natural and synthetic plant-growth substances 

 accords with that of vitamins and hormones in animals. Very 

 small quantities of either of the latter suffice to exert an optimal 

 action upon the animal organism. The quantitative similarity 

 is strengthened if the animal doses are calculated per gram 

 instead of per kilogram of body-weight as usual. The animal 

 is to some extent protected against overdosage of vitamins by 

 the necessity of ingesting them through the gut. The plant 

 itself has no obvious protection against excess of auximones 

 offered to it in water solution, but it is possible that the 

 colloids of manure and of soil are the plant's defence in this 

 respect. 



Chemical Constitution and Phytological Activity 



The following compounds (three of which are heterocyclic) 



have been shown to possess varying degrees of phytological 



activity, when provided with an acetic-acid side-chain. 



(R= — CH2.COOH). The names under the formulae are 



^R 



vV 



N 



indolyl- 

 (various) 



/v 



coumaryl- 

 Thimann 



A 



A 



VV-" VV W 



CH 



indenyl- 

 Thimann 



"thio-naphthenyl- 

 Shackell 



82 



