64 



investigators. Laurent further finds that the tubercle organism can be 

 cultivated successfully in solutions containing no nitrogen, thus con- 

 firming results which had i)r('vious]y been obtained by Prazmowski and 

 lir»'al, and adding a signiticant fact to our knowledge of the relation of 

 these microbes to atmospheric nitrogen. Although the tubercle organ- 

 isms certaiidy grow in nitrogen-free solutions, Laurent has as yet been 

 unable to show by analysis that they actually fix nitrogen from the air, 

 on account of tin; small amount of nitrogen present in such cultures. 

 Summary. — From this brief review it will be seen that our i)resent 

 knowledge of the functions of the root tubercles is somewhat as follows : 



(1) Tlie tuberch'S arc produced by organisms which ordinarily live in 

 the sod, especially' in soils in which legumes have previously been 

 grown. It is not yet definitely determined whether different species of 

 mi(;robes are associate*! with difi'erent species of legumes. 



(2) The tubercles are undoubtedly in some way connected with the 

 I)Ower of the plant to acquire nitrogen from the atmosphere. Their 

 presence enables the legumes to accumulate nitrogen when growing in 

 a nitrogen-free soil, and jirobably increases the nitrogen assimilation 

 in all soils. 



{'.V) The nitrogen assimilated comes from the atnuisphere. In all 

 pi-obability the free nitrogen of the air is thus assimilated. 



(4) It has not yet been determined whether the microbe itself 

 deiives the nitrogen from the air aiul is then used by the plant for food, 

 or whether the power of assimilating nitrogen belongs to the plant and 

 is only stimulated by the microbe, or whether this power is a function 

 of the combined life of tiie two organisms growing together. 



New experiments concerning the assimilation of nitrogen by plants, B. 

 Frank and R. Otto {Pnil. laiidic I'res.sc, IS (18!»1), ;>. 4(K?).— Determina- 

 tions of the nitrogen in the leaves of red clover, lucern, wood jn-a, cole 

 rape, hemp, grape, caraway, and jellow lupine, collected from growing 

 plants in the morning and in the evening and immediately dried at (JO*^ 

 C, showed the leaves collected in the evening to be richer in nitrogen 

 in every case than those collected in the morning. The difference was 

 most ]U'ominent in the cases of lucern, red clover, and wood pea. The 

 percentages of nitrogen found in the leaves of these plants, calculated 

 for dry matter, are given as follows: 



In other experiments the influence of sunlight on the nitrogen content 

 of leaves after cutting, was observed. Leaves of red clover and yellow 

 lui)ine were gathered in the morning, and while a part of them were 

 dried immediately at GO'^ C, the remainder were placed with their stems 



