910 EXPERIMENT STATION RECORD. 



lar treatment of other saccharine bodies results in the production of 

 tartaric acid. Plant acids are due to a partial oxidation of neutral sub- 

 stances. When the carbohydrates oxidize at a low temperature or the 

 penetration of oxygen into the tissues of the plant is interfered with 

 by the structure of the organs, combustion of the neutral substances is 

 not complete, i. e., they are.not reduced to carbon dioxid and water. In 

 this case the oxygen combines with the substances to produce the acids. 

 For example, considerable amounts of oxalic acids and oxalates are 

 found in the juice of the cactus, especially the prickly pear, which is 

 but slightly permeable to air. When, therefore, the volume of oxygen 

 absorbed is greater than the volume of carbon dioxid evolved it may be 

 assumed that oxygen has been fixed by organic compounds in the plant 

 to produce acids. These acids, then, are derived from neutral sub- 

 stances by oxidation, and, consequently, trace their ultimate origin to 

 the decomposition of the carbon dioxid in the chlorophyll cells. 



ORIGIN OF THE NITROGEN IN PLANTS. 

 ORIGIN OF THE NITROGEN IN LEGUMINOS.E. 



In the experiment to which attention was called at the beginning of 

 this article it would have been impossible to grow peas without adding 

 a few cubic centimeters of an infusion of fertile soil to the sand. If 

 this precaution were not observed with the peas or if the seed of some 

 nonleguminous plant were used the experiment would be a, failure. The 

 seed would produce a sickly plant which would soon die of starvation 

 due to the absence of one of the elements — nitrogen — necessary to its 

 development. Although the leaves of plants grow in an atmosphere 

 four-fifths of which is nitrogen they are entirely incapable of directly 

 utilizing this element. 



The process by which the free nitrogen of the atmosphere is utilized 

 by plants has only been explained in comparatively recent years. 

 Hellriegel and Wilfarth in 1880 reported experiments which demon- 

 strated the ability of Leguminosa' to attain normal development in soil 

 absolutely deprived of organic matter, the only precaution necessary 

 being the addition of a small amount of an infusion of fertile soil. A 

 few weeks after the addition of the infusion the roots of the leguminous 

 plants were covered with tubercles which microscopic examination 

 showed to be filled with micro-organisms. Breal has shown that inocu- 

 lations may readily be made with these organisms by pricking a 

 tubercle with a needle and then inserting it into a growing root. 



The tubercle bacteria have been cultivated and their products have 

 recently been brought into commerce under the name of "Nitragin," 

 which is used for supplying these organisms to soils which are deficient 

 in them. The growth of leguminous plants in sterile sand depends 

 upon the presence on their roots of tubercles filled with these organ- 

 isms. Through their agency the plant is supplied with nitrogen for 



