86 



GENERAL SCIENCE 



gen has neither color, odor, nor taste. Due to the fact 

 that it unites so reluctantly with other elements, it is 

 used in all of our common explosives, such as gunpowder, 

 dynamite, and nitroglycerine. 



Nitrogen has a very important work to do in the man- 

 ufacture of proteins by the plants, but just how this 

 takes place is not well known. The plant seems to add 



nitrogen and other elements 

 to the carbohydrates. These 

 foods are taken into the 

 plants in the form of solu- 

 tions in ground water, but 

 there are a few plants that 

 seem to take up nitrogen di- 

 rectly from the air. These 

 are such plants as beans, 

 peas, alfalfa, and clover. This 

 power is due to certain bac- 

 teria or very small plants 

 which attach themselves to 

 the roots (Figure 87) and, 

 taking the nitrogen from the 

 air, build it into certain 

 albuminous foods which the plant can use. The growing 

 of crops of peas, beans, clover, and alfalfa is very bene- 

 ficial to the soil, since these little bacteria take more 

 nitrogen from the air than the plants to which they are 

 attached need, and therefore, when the plant dies, an 

 excess of valuable nitrogen is left in the soil for other 

 plants to use. Farmers often grow such crops simply 

 for the purpose of enriching soil which has become im- 

 poverished through the raising of other crops. Artificial 

 fertilizers which contain nitrogen compounds are also 



FIG. 87. Roots showing Nitrogen 

 Tubercles. 



