733 



The experiments as to the relation of kind of soil to the assimilation 

 of nitrogen were made Avith rape and oats grown in sand and loam; 

 and with lupine, peas, and red clover grown in sand, hamus soil, and 

 moor soil, varionsly fertilized. Parallel experiments were made in all 

 cases, one set of plants being inoculated and another uninoculated. 

 Tlie resnlts of this series of experiments are given, together with the 

 summary of tliose relating to species and plant food supply, in the fol- 

 lowing general conclusions, which are by the author: 



(1) All plants, uoii-l('<j;uniin()ii.siis well as lojjnininoiis, can ntilizolhc froe nitrogen of 

 till! ail' ; in other words, a <;r(!atcr or less ])art of the nitroj^cii contained in the harvested 

 cro]) has been derived hy the plant from the air. The assimihition of free atmospheric 

 nitrogen is a physiologieal function of all plants, without regard to class or order. 



(2) While the combined nitrogen of the soil is not to be altogether ignored, its 

 importance in the cultivation of jilants differs Avidely with different kinds of plants. 



(3) So far investigaf ions have pointed to only one plant, namely, the yellow lupine, 

 ■which when inoculated with its special tubercle microbes and grown in soil free from 

 or poor in nitrogen, yields a larger amount of nitrogen iu the harvested crop without 

 nitrogenoxis manures than with them. That is to say, iu the case of this plant 

 grown on light soil the symbiosis alone is more effectual in inducing nitrogen assimi- 

 lation than the symlnosis and nitrogenous manures used together. The latter 

 appear to diminish the ability of the j)lant to acquire atmospheric nitrogen, and 

 hence are a direct waste. 



(4) The i)ea, on the contrary (and probably many other Leguminosic), gives the 

 maximum yield of nitrogen when nitrogenous manures, especially nitrates, are applied 

 in addition to the symbiosis. The quantity of nitrate required, however, is less than 

 has usually been supposed necessary. 



(5) The yellow lupine is out of place ou rich soils, as with the symbiosis it yields 

 less nitrogen there than when grown on soils poor in nitrogen. 



(6) Peas, red clover, and probably many other Leguminosa? yet to be tested 

 obtain more nitrogen from the air when grown ou rich humus soils than when grown 

 on lighter soils, even though the latter be manured with sufficient phosphoric acid 

 and potash. Since the nitrogen in the soil seems to be a controlling factor in the 

 case of these plants, it is a question whether rich soils require nitrogenous manures 

 lor these crops. 



(7) The stubble and roots of leguminous plants enrich the soil in nitrogen to a far 

 greater degree than those of non-logumiuous plants, especially in proportion to the 

 amounts of nitrogen which they derive from the soil. The latter, however, take a 

 part of their nitrogen from the air and their effect in enriching the soil is seen if the 

 •whole plant is returned to the soil. This effect is more prominent the better adapted 

 the soil is to the crop and especially if a supply of readily available nitrogenous fer- 

 tilizer is fiirnished during the earlier stages of growth. 



(8) Both leguminous and non-leguminous plants agree iu that the reserve supply 

 of nitrogen in the seed is insufficient to supply the young plant until it reaches the 

 stage whore it can assimilate sufficient nitrogen from the atmosphere, and unless 

 nitrogen is furnished to bridge over this interval nitrogen hunger ensues. 



(9) In the case of non-leguminous plants the nitrogen hunger is avoided by apply- 

 ing sufficient nitrogenous fertilizer to the soil to enable the plant to reach the stage 

 where it can assimilate atmospheric nitrogen. In leguminous plants, however, this 

 younger stage is provided for by the presence of certain bacteria which render 

 atmospheric nitrogen available to plants of this order during this stage of develop- 

 ment. These bacteria render leguminous plants independent of combined nitrogen. 



(10) Nitrogen assimilation occurs in non-leguminous plants without the aid of 

 microbes, and these are not absolutely es.jcutial in leguminous plants, for if the 



