308 SYMBIOTIC NITROGEN FIXATION 



sort of change, produce the substance containing the assimilable 

 nitrogen which the plant used. 



There appears to be considerable evidence in favor of this second 

 theory. Stefan thinks that the transfer of the assimilable nitrogen 

 from the organism to the host plants follows the ordinary physical 

 laws of osmosis, and Golding has conducted some very interesting 

 experiments on the removal of the products of growth in the assimila- 

 tion by nitrogen by legume bacteria. He reasoned that the plant 

 played an important role in the removal of the products produced by 

 bacteria in the nodules aside from the mere furnishing of suitable 

 food. He used a porous Chamberland filter candle placed in a 

 culture vessel to serve to imitate natural conditions. The parts of 

 the plants used in some of his experiments were sterilized in order to 

 avoid the possibility of plant enzyme action. As a result of his 

 method of experimentation he obtained a much greater fixation of 

 nitrogen than other experimenters had obtained. He concluded that 

 the plant plays a part in the removal of soluble products of growth, 

 thus permitting a more rapid reaction than where the products 

 accumulate. 



The results of Golding's most extensive experiment are sum- 

 marized as follows: 



Nitrogen in 

 Grams. 



500.0 gms. of steins and leaves 2.865 



26. 2 gins, of roots and nodules (quite fresh) 0.094 



3000.0 c.c. ammonia-free distilled water 0.000 



Total nitrogen to start with 2 . 959 



2870.0 c.c. filtrates and drainings ., 0.731 



566.2 gms. wet residue . 2.570 



Total nitrogen after experiment 3.301 



Total gain of nitrogen during experiment 0.342 



Attempts have been made to obtain an insight into the transforma- 

 tion going on in the nodules by various analyses. These have been 

 summarized by Whiting as follows : 



"Chemical The chemical composition of legumes from the 

 standpoint of their nitrogenous constituents has been investigated 

 to some extent, but the studies closely related to this point are 

 relatively few. The following data are very general in character 

 and relate to studies concerning the total nitrogen content of the 

 different parts of legumes at different periods of growth. Studies 

 upon some of the various nitrogenous compounds are also included. 



"In 1895 Stoklasa, working with lupines (Lupinus luteus and L. 

 ajigustifolius) , found that the nodules were richest in the element 

 nitrogen at the time of blooming, while the roots appeared to be 

 richest in that element at the fruiting period. His results are given 

 in Table I. The figures for the nodules indicate the nitrogen is 

 either taken up by the plant for seed production or diffused into the 

 soil. 



