VAUGHAN ON VALUK OP SCIENTIFIC RKSEARCH TO STATE. 27 



SO bad as was once believed. He has demonstrated that there are certain 

 niicioorganisnis growing on the roots of certain plants, and that by the 

 combined action of the germ and the i)lant free nitrogen may be taken 

 from the air and utilized in building up plant tissue or in other words, 

 that it may be changed from the free to the combined form, and when 

 thus changed it may subsequently be used for food by either plants or 

 animals. This is what is known as the T)rocess or function of lixing 

 nitrogen, and it depends upon the combined action between certain germs 

 and leguminous plants. About twenty years ago it was quite conclu- 

 sively shown that peas, beans, and otlier legumes when grown in a poil 

 wholly free from nitrogen were capable of constructing nitrogenous com- 

 pounds and building up nitrogenous plant tissue, while the only source 

 of the nilrogcn thus utilized was that existing free in the atmosythcre. 

 At first this view was believed to be founded upon faulty observations, 

 but thorough experimentation has shown that the statement made above 

 is a fact. Then men set about to ascertain the conditions under which 

 plants, and especially leguminous plants are able to utilize the free 

 nitrogf^n of the atmosphere. These experiments were conducted by skilled 

 botanists in various parts of the world, and now after twenty years of 

 these labors it can be positively stated «that the manner in whirli legumi- 

 nous plants convert nitrogen into compounds has been discovered. If 

 the roots of a leguminous plant be studied they will be found to be dotted 

 with tiny nodules, which are known to the botanist as tubercles but 

 which, however, have no relation to the pathological conditions known 

 to the medical man under the same name. These tubercles or swellings 

 on the roots of the pea vine vary markedly in size. They may be so small 

 that they are bnrely discernible to the naked eye, and in some instnnces 

 they have a diameter of one-sixth of an inch or more. Of course the 

 existence of these nodules on the roots of leguminous plants had been 

 long known, but their function was not understood. It w.as generally 

 believed that their presence indicated a diseased condition, but it was 

 found that the plants on the roots of which they developed most abun- 

 dantly thrived most vigorously. I shall not attempt before this audience, 

 in which there are manv who know more about this subject than T do. to 

 go into detail concerning the relation of these tubercles to the fixation 

 of nitrogen by leguminous plants. Suffice it to say that exoerimentation 

 has shown that these nodules do not form on the roots of plant*^ grown in 

 sterilized soils, and that under the same conditions such plants take up 

 no nitrogen from the atmosrdiei^e. Next it was found that if legumin(ms 

 seeds were planted in sterilized soil, devoid of nitrogenous food, and were 

 watered with an infusion of sterilized soil, they manifested two character- 

 istic and pecul'ar stages of growth.- At first the peas sprouted readily 

 and grew vigorously for a very short time, when growth ceased. Tliis 

 j)eriod, which the botanist now designates as the stage of nitrogen hun- 

 ger, was reached as soon as the plant had used up all the combined nitro- 

 gen in the seed. If at this stage some of the plants were watered only 

 with sterilized earth infusions they did not recover, but continued to 

 wn«!te away an^l finally died, while those watered with non-sterilized soil 

 infusions soon began to take on a vigorous growth, eventually develo])ed 

 into well nourished plants, and produced an abundant yield. Upon ex- 

 amininir the roots of these two sets of plants it was found that those 

 watered with sterilized soil infusions showed no tubercles or nodules, 



