662 PROCEEDINGS OF SECTION K. 



While conducting some water-culture experiments at Rotham- 

 sted, in 1906, certain results were obtained by the author which 

 seemed to corroborate this theory in a rather striking manner. In 

 one series of experiments, in which all the mineral ingredients of 

 the plant's food material were supplied in about the usual propor- 

 tions for water-cultures, the barley plant grew to maturity and pro- 

 duced grain. Where any one of the essential ingredients was 

 omitted the plants, as was anticipated, failed to develop normally 

 and succumbed at an early period of their growth. My interest 

 was aroused by the fact that the barley plant growing m the solu- 

 tion from which the solvible phosphate was omitted differed from 

 the others in that it made practically no root-development, 

 although its stem and leaves grew quite vigorously for a time (Fig. 

 1.) A new series of solutions was therefore made up containing 

 varying amounts of phosphoric acid together with normal amounts 

 of the other essential ingredients. Barley was again grown in each 

 cylinder with the results shown in the photograph (Fig. 2). 



The quantities of phosphoric acid varied from one-tenth to 

 twice the usual amount employed in water-cultures, and it will be 

 seen that the effect of increasing amounts of phosphoric acid was 

 much more marked on the development of the roots than on the 

 portions of the plant above what would correspond to ground level. 

 As it is very unwise to draw conclusions from water-cultures alone, 

 sand culture experiments of a similar nature were prepared — 

 di-calcic phosphate being used in this case as a source of phos- 

 phoric acid. The roots and shoots of the barley plants grown were 

 cai-efully weighed in each case, with the result that each successive 

 addition of phosphate was found to cause a distinct increase in the 

 weight of the roots and a still greater increase in the weight of the 

 stems and leaves. This was not taken as a proof that the theory 

 of direct stimulus was wrong; for, when other conditions are favor- 

 able, it is probably impossible to increase the amount of the absorb- 

 ing surface of the -roots without increasing even more the vegetative 

 part of the plant above ground. My departure for South Africa 

 early in 1907 prevented the investigation from being carried fur- 

 ther at the time ; but the subject again attracted my attention on 

 the occasion of my first visit to the wheat-belt of New South Wales, 

 where the remarkably beneficial effect of the application of com- 

 paratively small amounts of superphosphate to the wheat crop came 

 under my notice. 



Even when due allowance is made for the comparative poverty 

 of Australian soils in phosphoric acid, the result seems to me much 

 more striking than I could have anticipated from my experience of 

 fertilizer experiments in other countries, though I had observed 

 somewhat similar, though less pronounced, effects on maize in the 

 Transvaal. One would naturally expect the normal limiting factor 



