72 TREE PLANTER'S MANUAL. 



contained in them is gradually converted into salts of nitric acid or nitrates, 

 and if the decomposition takes place in the air, the nitrogen is converted 

 into ammonia." 



Prof. Snyder, of our Experiment Station, says: "Nitrogen supplied for 

 plants and crops is the most important factor, economically considered, of 

 all the elements that are necessary for plant food." 



HOW PLANTS GET NITROGEN FROM THE AIR. 



Botanists have of late discovered that the little nodules or tubercles on 

 the roots of pines, oaks, willows and many other trees, also on those of 

 leguminous plants, such as the clovers, peas, beans, lupines, etc., so far 

 from being evidences of disease, are root-ganglia, so to speak, developed 

 by a species of bacteria, by which the plant gets its atmospheric nitrogen. 

 Prof. E. W. Allen, assistant director of the office of Experiment Stations, 

 Washington, D. C. , applies this important discovery to agriculture, bulletin 

 16, p. 6: "It is sufficient for practical purposes to know that nitrogen is 

 taken up from the air by the growing plant, directly or indirectly; and that 

 this nitrogen assimilation takes place as a result of the life of bacteria. It 

 is a peculiar fact that few, if any, root tubercles are formed when legum- 

 inous plants are manured with nitrogen; the plants must first hunger for 

 nitrogen before the tubercles are formed, and the presence of tubercles 

 indicate that the plant is taking nitrogen from the air." After showing 

 the necessity of aiding crops by "soil inoculation," a light dressing of 

 soil "in which the kind of plants it is wished to grow have been previously 

 grown," he urges enriching the soil with nitrogenous elements by green 

 manuring of plants producing them, clovers especially. "It will thus be 

 seen that by green manuring with leguminous crops it is possible to manure 

 the soil with nitrogen from the air, a free and inexhaustible source, and 

 thus avoidbuying fertilizers containing much nitrogen. This greatly lessens 

 the expense for commercial fertilizers, for nitrogen is the most expensive 

 element the farmer has to buy." 



CORRELATION OF AGRICULTURE WITH FORESTRY. 



In the cases cited we learn, in a new light, the delicate correlation of 

 agriculture with forestry. What the intelligent farmer does with the 

 green manure of leguminous plants whose nitrogenous properties they have 

 extracted from the air, nature is constantly doing in her massive forests 

 where the spoiler hath not trod. She manures the forest soil with green 

 and ripened leaves; they form a perfect mulch that economizes the moisture 

 which the trees must have; they oxidate and decay next to the surface soil, 

 whence is evolved the needed nitrogen for plant growth. Thus the roots 

 by a chemical art that we cannot fathom, take up the primates of the 

 mineral kingdom and transform them into living tissue. If on this pro- 

 gressive line there is yet a deficiency of nitrogen for healthful assimilation, 

 the lower forms of life, bacteria generated by these processes, build ganglio- 

 batteries on the famishing roots, and the trees are re-invigorated for 

 woody structure. This chemical operation, whereby pure oxygen is tendered 

 us, prepares a soil for future agriculture, rich in nitrogenous and other nee- 



