In preparing cultures it has been found that by gradually reducing the amount of nitrogen in the culture of media, it is possible to increase the nitrogen fixing power in these germs from five to ten times as much as usually occurs in nature. It is now known that the bacteria thus grown upon nitrogen free media retain high activity if carefully dried and then revived in liquid media at the end of the varying lengths of time. Some absorbent is used to soak up the tubercle-forming organisms. The cultures are then allowed to dry, and when in that condition they can be safely sent to any part of the country without losing their efficacy. It is necessary to revive the dry germs by immersing them in water. By adding certain nutrient salts the bacteria are greatly increased if allowed to stand for a limited time--as short, in some instances, as 24 hours. The culture thus sent out in a dry form, and no larger than a yeast cake, may thus be made to furnish bacteria sufficient to inoculate not less than an acre of land. It is stated that the amount of inoculating material thus obtained is only limited by the quantity of the nutrient water solution used in increasing the germs, so that the cost of inoculating land by this process is not large. The culture may be applied by simply soaking the seed in it, by spraying the soil, or by first mixing the culture into earth, spreading it over the field and then harrowing it. Inoculations thus tried under the supervision of the United States Department of Agriculture have proved quite successful. Where any legume is extensively grown surrounding soils come to be inoculated through the agency of winds and water. The increase brought to the yield of plants on various soils runs all the way from a slight gain to 1000-fold. And when soil is once inoculated it remains so for a long time, even though the proper legume should not be grown again on the same soil. The amount of nitrogen that may thus be brought to many soils by growing clover and other legumes upon them is only hedged in practically by the nature of the rotation fixed upon. An acre of clover when matured will sometimes add 200 to 300 pounds of nitrogen to the soil under favorable conditions. Where the soil contains the requisite bacteria, the young plants begin to form tubercles when but a few weeks old, and continue to do so while the plant is active until mature. That the plants use much of the nitrogen while growing would seem to be clear, from the fact that toward the close of the growing season the tubercles become more or less broken down and shrunken. CHAPTER III MEDIUM RED CLOVER