Plant Qrowth'Suhstances 



covery that indole-acetic acid had growth-regulating pro- 

 perties. Whilst the auxins were new to science, indole-acetic 

 acid, and substances chemically similar to it, have been 

 known for a long time. A number of ways of artificially pre- 

 paring indole-acetic acid and its relatives were already known 

 before Kogl found the acid to be a growth-substance. It did 

 not take long to test the growth-regulating properties of it and 

 of other substances like it. It was found that a solution of 

 indole-acetic acid, for example, when painted on the stem of 

 a tomato or other soft-stemmed plant caused roots to grow 

 on the stem. From that it was but a step to the attempt to 

 quicken root-formation on cuttings. It was found that 

 indole-acetic acid did considerably hasten the appearance of 

 roots on cuttings put into compost. Hence, it and its relatives 

 are already of practical importance as an aid to horticul- 

 turists and gardeners. A number of the artificial growth- 

 substances, including indole-acetic acid itself, are now on sale 

 for horticultural purposes. 



If you are a business man or woman, you will perhaps think 

 that here is a field to exploit, by selling manures to which 

 traces of the growth-substances have been added, while you 

 claim remarkable properties of growth-promotion for "Smith's 

 Auxonic Fertilizer". The idea has already occurred to a 

 number of people, but I think that to translate it into practice 

 without more knowledge of the modes of action of growth- 

 substances would be to start at the wrong end. In my view, 

 it is more important to investigate the old, well-tried, organic 

 manures of the farm, and to see whether they contain the 

 growth-substances, and in what proportions. If growth- 

 substances are present in organic manures, a knowledge of 

 their presence and distribution may help us to understand 

 more about soil fertility, and possibly about the healthfulness 

 of foods. Such research work on organic manures has hardly 

 yet begun, but a beginning has been made in America. 



Some years ago, the foundation of an understanding of the 

 rotting-down of organic materials was laid at Rothamsted, 

 during an investigation of the decomposition of straw. One 

 practical result was the production of the so-called artificial 



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