194 



PRESIDENT S ADDRESS. — SECTION G. 



at au efficieint level, or toi bring laud which is not sufl&ciently 

 fertile in the ordinary course, than to give an increased yield.* 



The electrical, biological, and other stimulation of plant growth, 

 biological selection, improvements by hybridization, &c., may, 

 of course, very materially increase the food supply, but whatever 

 be achieved, there is noi escape ultimately from the law of 

 diminishing returns for a given increase of eifort. For this reason 

 the tendency will always be for population tO' advance faster than 

 food supply, and the notion that this can be defeated is founded 

 on a misapprehensicn of the nature of the whole question. 



The questiorn of futurei water supplies for cities is also one of 

 moment. The systematic conservation of meteoric waters has 

 already done much to facilitate the earth's carrying a larger 

 population. The exploitation of artesian supplies has also 

 operated in the same way. In the latter case, however, a change 

 from the artesian to the sub-artesian condition has shown that the 

 value of such sources is very limited indeed. Already, too, diffi- 

 culties are arising in towns through the advancing needs of their 

 rapidly growing populations. The provision for large cities, 

 ordinaril}- dependent on catchment areas so^me distance off, is now 

 becoming a .serious problem for many of them. In order to give 

 an idea as toi the rapid rate in which the consumption has increased 

 even here, in Sydney the average daily supply rose from 8,000,000 



* The following table shows that the quantity per acre of artificial manure used is freely constant 

 while that of natural manure is decreasing. 



cosimonwealth — area under crop (>iainly cereals) : area manured, and quantity of 

 Manure used, showing Quantity used per Acre of Total Area Manured. 1907 to 1918. 



The horizontal lines indicate a break in the continuity since the State of Tasmania is for the 

 first time included in 1913. and Queensland for the flr.st time in 1915. The percentage of " area 

 under crop " manured, and amounts per acre under crop, may be regarded as continuous. 



