238 



METABOLISM 



that he noticed a gain in nitrogen, Maze, finally, used proteid, believing that 

 the Bacteria in the first instance, doubtless, obtained it from the plant. His 

 results were striking : — 



1. 



Nitrogen in the culture solution 6a-i mg. 



Nitrogen at the end of the experiment loag ,, 



II. 

 70-7 mg. 



tl8-2 ,, 



III. 

 23-4 mg. 

 45-8 „ 



Gain in nitrogen 408 mg. 475 mg. 23-4 mg. 



[Maze's results have been questioned by Hiltner (1904).] 



In addition to nitrogen in the form of proteid. Bacterium radicicola uses 

 up very considerable quantities of sugar, and we must conclude that both 



Fig. 42. Entry of Bacteria into the roots of Legumi- 

 nosae. a, cortical cells of the root of the pea, containing 

 tubular masses of Bacteria, x 650 ; b, roothair of the 

 pea, on the left of which a number of Bacteria have 

 accumulated outside. Apically the Bacteria are seen 

 mixed with the protoplasm of the hair, whence the 

 infecting threads are proceeding inwards to form the 

 tubular Dacterial aggregates, x 175. From Fischer 

 (Vorles. ii. Bakt. and ecd.). 



Fig. 43. Root nodules of Leguminosae. a, root 

 nodule oflupin, nat. size; 6, longitudinal section of the 

 same, several times magnified (^, vascular bundle ; w, 

 bacteroidal tissue); c, bacterial cells of lupin(the Bacteria 

 are indicated as black dots, x 600) ; d, Bacteria of 

 lupin ; e, bacteroids of yicia villosa ; f, bacteroids of 

 Litpinus albus ; d-f x 2500. From Fischer (Vorles. 

 ii. Bakt. 2nd ed.). 



substances are provided by the leguminous plant, sugar continuously and 

 proteid only at the beginning, since obviously the fixing of atmospheric nitrogen 

 commences after a certain time. 



Since, in the end, the bacterium yields nitrogen to the leguminous plant, and 

 the latter yields carbon in an appropriate form to the bacterium, we may speak 

 of the union of the two organisms as a case of symbiosis. It is true the associa- 

 tion has been otherwise interpreted ; Fischer (1903), for example, considers 

 the leguminous plant as a parasite on the bacterium, but this does not appear 

 to us to be a correct view to take. 



It is quite probable that in the foregoing exposition of the phenomenon 

 of nitrogen assimilation in Leguminosae there will be found many omissions. 

 Indeed the researches of Hellriegel and Wilfarth prove only indirectly 

 that the nitrogen of the air is combined ; they show a gain in nitrogen, and 

 demonstrate that the air is the only source whence that element could have 



