Chap. Page 



VI The treatment of seeds _ - - - 46 



References C------49 



VII The use of synthetic substances in various 



horticultural and other operations 

 Grafting; rooting of grafted cuttings - - 51 

 Inhibition and stimulation of budding and 



flowering; forcing - - - - - 53 

 Possible non-biological applications - " 57 



References D------57 



VIII What is a root? 59 



IX Growth-substances from natural sources 



Agricultural researches having a possible 

 bearing on growth-substances in soil and 

 manure -------62 



Vitamins -------68 



References E------69 



X Some constituents of urine. Occurrence of 

 growth-substances (other than the auxins 

 and vitamins), and bodies related thereto, in 

 urine ------- yi 



XI Chemistry in relation to growth 



Some notions on concentrations - - - 77 



Inhibition and stimulation - - - 77 



Plant growth substances in tissue culture 81 



Chemical constitution and phytological activity 82 



References F------89 



XII Classification and nomenclature of growth sub- 

 stances -------91 



What a hormone is - - - - 92 



Group nomenclature for plant growth- 

 substances ----- 95 



References G - - - - - 97 



viii 



