57 



attnosplieric iiitrop;en inip:lit be aidoil.* Otlicr cxin'iimeiiters, inclii<l- 

 iiij^- ni'lliu';i,('l iuid Wilfaitli, Wolll', Ureal, and Lawcs and Gilbfit, 

 have since vviifuMl the conclnsions tluns iep(»it<'(l in 18S1-84. To <lay 

 it is generally accepted that legumes at least accinire large amounts of 

 atmospheric nitrogen. The leaves perhaps may be unable to absorb 

 tills element I'rom the air, but the indications have been growing that 

 the roots of the plant do in some way obtain large (piautitiesof nitrogeu 

 from the atmosphere. 



The relaiion of the root tubercles to the acquisition of atmospheric 

 nitrogen was first suggested by Ilellriegel, who was aided in his work 

 by VVilfarth. Their results were published in two papers.t Ilell- 

 riegel found that the Gramiuea>, and the Leguminosea; difler radically 

 from eacii other in their relation to nitrogen. The former can not flour- 

 ish in a soil devoid of nitrogenous comi)aunds. For a short time they 

 grow readily enough, but as soon as the material supplied in the seed 

 is used np the plants begin to turn yellow, become stunted, and never 

 show ati}- increase in nitrogen over that contained in the seed. They 

 are, in fact, nitrogen-starved, for if nitrogen is added to the soil at the 

 time that the starvation period begins, a recovery takes place. The 

 Graminea' are unable to make use of atmosi)heric nitrogen. With the 

 leguminous plants, different results were obtained. lu experiments 

 with i)eas, Ilellriegel verified previous observations by finding that 

 these plants do undoubtedly gain nitrogen from the atmosphere. He 

 observed that when they were grown in soils consisting of pure quartz 

 sand thoroughly freed from nitrogen compounds, and fed with materi- 

 als containing no nitrogen, the i)lants nourished and eventually showed 

 a considerable increase in nitrogen. In the growth of these plants in 

 nitrogen-free soil he found two marked stages. The develoi)ment is 

 rapid at first, and continues until the reserve material in the seed is 

 exhausted. Then there occurs a somewhat sudden cessation of growth, 

 similar in character to the starvation period observed in Gramine;c. 



In the case of the legumes, however, the plant soon recovers; its 

 leaves turn green again, the growth goes on in a normal manner, :'.nd 

 final analysis shows that nitrogen has been accumulated. Consider- 

 able variation was noticed in the growth of plants under these condi- 

 tions, even though all were treated seemingly alike. Of two plants 

 growing side by side, one was sometimes vigorous and the other dwarfed 

 and stunted. The vigorous plants all had tubercles on their roots, while 

 the others either had none or relatively few. The recovery of the plants 



* The results of the expcriinonts of tlio first series were briefly reported at the 

 nieotiiijf of tlie American Association for tiie Advaucemoiit of Science in IS-^l; tliose 

 of the lirst and second series to<;ether were reported at the meetings of the British 

 and American Association for tlio Advancement of Science in l""'d4, and in detail in 

 the American Chemical Jonrnal. vol. vi, p. :?();"), and those of the later series in the same 

 journal, vol. \iii, pp. :V27 and '.VM. 



tTagebl. d. ;")•) Versamml. dent. Natnr. fii. Aerzte, Wiesbaden, LS"^", and Zeitsch. d. 

 Ver. f. Kubeuz. lud. d. d. K., 1886 and 188d. 



