Early Experience with Legumes 241 



cline. The exhaustion of lime and of available phos- 

 phoric acid in the older soils of Europe made the growth 

 of beans and peas uncertain. Their cultivation was 

 much reduced or entirely abandoned on thousands of 

 farms, and the use of bare fallows greatly extended. 



In the seventeenth and eighteenth centuries, there 

 came a revival in European agriculture. Marling and 

 liming again made possible the growth of legumes. 

 Clover was introduced and proved a boon to the impover- 

 ished soils. Regular rotations were evolved, and hoed 

 crops like turnips became more prominent. The time 

 came later when clover failed more and more frequently, 

 until gypsum and, subsequently, artificial fertilizers, were 

 found to be a partial or complete remedy for the diffi- 

 culty. Finally, the discovery of the nodule-bacteria 

 and the explanation of their true functions led to the 

 development of rational methods of farming, by which 

 the nitrogen of the air is systematically utilized by means 

 of leguminous crops and is made to supply the needs of 

 non-legumes. 



Green-manures on sandy soils. Green-manuring has 

 found a wider sphere of usefulness and more thorough 

 utilization on light sandy soils. This is accounted for 

 by the greater poverty of such soils, their openness, 

 their inability to hold sufficient moisture for the best 

 development of crops, and their lack of humus. Theoreti- 

 cally, at least, these soils could be improved by the ad- 

 dition of fertilizers. But, because of their very open 

 character, the proportion of plant-food lost from them 

 would be considerable. The addition of something that 

 will help to hold in the soil not only the plant-food, but 



