570 



SCIENCE. 



[N. S. Vol. VIII. No. 200. 



ished doctrine bear the test of examina- 

 tion? 



Cheap production of wheat depends on a 

 variety of causes, varying greatly in diiFerent 

 countries. Taking the cost of producing a 

 given quantity of wheat in the United 

 Kingdom at 100s., the cost for the same 

 amount in the United States is 67s., in 

 India 66s., and in Russia 54s. "We require 

 cheap labor, fertile soil, easy transportation 

 to marliet, low taxation and rent, and no 

 export or import duties. Labor will rise 

 in price, and fertility diminish as the requi- 

 site manurial constituents in the virgin 

 soil become exhausted. Facility of trans- 

 portation to market will be aided by rail- 

 ways, but these are slow and costly to con- 

 struct, and it will not pay to carry wheat 

 by rail beyond a certain distance. These 

 considerations show that the price of wheat 

 tends to increase. On the other hand, the 

 artificial impediments of taxation and cus- 

 toms duties tend to diminish as demand 

 increases and prices rise. 



I have said that starvation may be 

 averted through the laboratory. Before 

 we are in the grip of actual dearth the 

 chemist will step in and postpone the day 

 of famine to so distant a period that we 

 and our sons and grandsons may legiti- 

 mately live without undue solicitude for 

 the future. 



It is now recognized that all crops re- 

 quire what is called a ' dominant ' manure. 

 Some need nitrogen, some potash, others 

 phosphates. Wheat preeminently demands 

 nitrogen, fixed in the form of ammonia or 

 nitric acid. All other necessary constitu- 

 ents exist in the soil ; but nitrogen is 

 mainly of atmospheric origin, and is ren- 

 dered ' fixed ' by a slow and precarious pro- 

 cess which requires a combination of rare 

 meteorological and geographical conditions 

 to enable it to advance at a sufficiently 

 rapid rate to become of commercial im- 

 portance. 



There are several sources of available 

 nitrogen. The distillation of coal in the 

 process of gas-making yields a certain 

 amount of its nitrogen in the form of am- 

 monia; and this product, as sulphate of 

 ammonia, is a substance of considerable 

 commercial value to gas companies. But 

 the quantity produced is comparatively 

 small ; all Europe does not yield more than 

 400,000 annual tons, and, in view of the 

 unlimited nitrogen required to substantially 

 increase the world's wheat crop, this slight 

 amount of coal ammonia is not of much 

 significance. For a long time guano has 

 been one of the most important sources of 

 nitrogenous manures, but guano deposits 

 are so near exhaustion that they may be 

 dismissed from consideration. 



Much has been said of late years, and 

 many hopes raised bj'' the discovery of 

 Hellriegel and Wilfai-th, that leguminous 

 plants bear on their roots nodosities abound- 

 ing in bacteria endowed with the property of 

 fixing atmospheric nitrogen ; and it is pro- 

 posed that the necessary amount of nitro- 

 gen demanded by grain crops should be 

 supplied to the soil by cropping it with 

 clover and ploughing in the plant when its 

 nitrogen assimilization is complete. But it 

 is questionable whether such a mode of 

 procedure will lead to the lucrative stimu- 

 lation of crops. It must be admitted that 

 practice has long been ahead of science, 

 and for ages farmers have valued and cul- 

 tivated leguminous crops. The four-course 

 rotation is turnips, barley, clover, wheat — 

 a sequence popular more than two thousand 

 years ago. On the Continent, in certain 

 localities, there has been some extension of 

 microbe cultivation ; at home we have not 

 reached even the experimental stage. Our 

 present knowledge leads to the conclusion 

 that the much more frequent growth of 

 clover on the same land, even with success- 

 ful microbe-seeding and proper mineral 

 supplies, would be attended with uncer- 



