PROCEEDINGS OF SECTION K. 



663 



iu the growth of wheat in the semi-arid districts of Australia to be 

 the failure of the plant to obtain an adequate supply of moisture 

 from the soil to satisfy the exacting requirements of a hot and dry 

 atmosphere, and of frequent scorching winds, and this has been 

 amply confirmed by my subsequent observations. In the light of 

 my previous experiments, it was therefore difficult for me to resist 

 the conclusion that part at least of the beneficial effect of super- 

 phosphate was due to its effect in increasing the depth of penetra- 

 tion, and consequently the surface area, of the moisture-absorbing 

 roots. It was found impracticable to separate and weigh the roots 

 of manured and unmanured wheat plants; so that my observations 

 have been confined to noting the greatest depth of penetration of 

 the roots of plants growing side by side, and treated in exactly 

 similar fashion, except that in one case the crop had received a 

 small dressing of superphosphate drilled in with the seed, and the 

 other had not. Advantage was taken of a visit to the experi- 

 mental farms at Wagga Wagga, Cowra, and Bathurst in the spring 

 of 1911 to make the first series of observations. The method of 

 procedure was to dig a trench nearly 18 inches wide, about 3 feet 

 long, and as deep as was found necessary, at the junction of 

 manured and unmanured plots, and to carefvilly scrape away the 

 sides of the trench so as to expose the roots with the following 

 results : — • 



Although every care was taken to select a suitable "location for 

 the observations, it cannot be denied that there was room for a 

 considerable amount of experimental error ; but it was noteworthy 

 that in each case there w^as a decided increase in the depth of root 

 penetration due to the application of superphosphate, and that 

 the contrast was greatest in the case of the younger plants. An- 

 other result which would, I think, surprise the average farmer was 

 that the roots of wheat grown under ordinary culture conditions 

 had penetrated to sucli a great depth as 34 inches into the red clay 

 subsoil at Wagga, in three and a half months after seeding, and at 

 a time when the plants were under a foot high, and 3 ft. 9 in. 

 into the stiff clay subsoil at Bathurst, when the wheat was only 

 four and a half months old, and about 16 inches above the ground. 



