NATURE OF PLANTS 67 



tioned that products and processes will be improved so as to meet 

 the rapidly increasing demands for nitrate. 



Much study has also been given to the nitrogen-fixing bacteria 

 as a further source of supply for nitrogen compounds. Failure 

 attended the numerous attempts to cultivate these important 

 plants with practical results, although our own department of 

 agriculture has met with a limited success in making cultures of 

 bacteria that are sold to farmers for mixing with their clover or 

 other leguminous seeds. See Bulletin 71, 1905, U. S. Dept. of 

 Agriculture. There are many difficulties in the way of intro- 

 ducing these forms, such as keeping them alive, supplying the 

 proper conditions for their growth and the variety of forms that 

 must be dealt with. Although there is possibly but one species 

 of these bacteria, they have become so changed through associ- 

 ation with the various kinds of leguminous plants that there are 

 numerous varieties, each adapted to one or a few species of plants. 

 Soils in one section may have the forms suitable for one kind of 

 plant and be totally deficient in forms required for other plants. 

 At present the only sure way of inoculating sterile soils is by 

 mixing with them soils containing the desired bacteria a labori- 

 ous and expensive method. Quite recently very promising 

 results have been obtained by growing the desired bacteria in 

 soils until they have so multiplied and permeated it that a small 

 amount of this soil will suffice to inoculate a large area. With- 

 out doubt means will be devised for cultivating the various forms 

 of these bacteria so that they may be sold for mixing with the 

 soil or seeds. Thus the farmer will be able to raise a crop that 

 contains a large amount of nitrogen derived from the air and by 

 plowing under this crop or better still, if conditions permit, by 

 feeding it to stock and utilizing the manure, he will be able to 

 add a valuable nitrogenous fertilizer to the soil. In this way the 

 soil is prepared for another crop, as wheat, which is dependent 

 for nitrogen upon nitrogenous compounds. This alternation of 

 crops is of prime importance in successful farming. Each kind of 

 plant takes from the soil certain elements in large amounts and 

 for this reason the alternating or succeeding crop should be of 

 such a kind as to require other elements. As these elements are 



