152 



THE EOTHAMSTED EXPERIMENTS. 



Gain of 

 nitrogen 

 by a non- 

 leguminous 

 plant. 



Various 

 nodule- 

 forming 

 bacteria. 



Form of 

 root-nod- 

 ules. 



Fuller 



evidence 



required. 



nitrogen by a non-leguminous plant, but only with the coin- 

 cidence of nodule-development on the roots. 



The conclusion drawn from the experiments of Nobbe — 

 that there are various nodule-forming bacteria — is at any 

 rate consistent with the descriptions which have been pub- 

 lished as to the difference in the external appearance, and the 

 distribution, of the root-nodules in the case of the peas, the 

 vetches, and the lupins, grown at Eothamsted. 



Again, the nodules on the roots of lucerne growing in the 

 field were observed at different periods of the season in 1887, 

 and again more recently on plants taken from the field for 

 that purpose ; and they are quite different in general external 

 character from those on any other plants that have been ex- 

 amined at Eothamsted. 



• Among the Leguminosse growing in the mixed herbage of 

 grass-land, in 1868 nodules were observed on the root-fibres 

 of Lathyrus pratensis, especially near the surface of the soil ; 

 on the ultimate root-fibres of Trifolium pratense ; and on the 

 smaller rootlets of Trifolium repens. In the case of red 

 clover growing in rotation on arable land, an abundance of 

 nodules has been found, both near the surface and at a 

 considerable depth. They are generally more or less globular 

 or oval. Some found on the main roots were more like 

 " swellings " than attached tubercles, not, however, encasing 

 the root, but only on one side. The greater number are, 

 however, small and chiefly distributed on the root-fibres. 

 Again, on the plot of rich garden-soil on which red clover has 

 now been grown at Eothamsted for forty years in succession, 

 very numerous nodules, chiefly globular and small, have been 

 found on the roots ; for the most part within the first few 

 inches of soil, but some to the depth of a foot or more, dimin- 

 ishing, however, very much both in number and in size as the 

 clayey subsoil was reached. 



Obviously much more evidence than is at present at com- 

 mand is needed in regard to any difference in character, or 

 relative prevalence, at different periods in the life and growth 

 of the plant, and under different conditions of soil, both so far 

 as mechanical state and porosity, and richness or otherwise 

 in available supplies of combined nitrogen, are concerned, be- 

 fore any clear conception can be attained of the connection 

 between nodule-formation, luxuriance of growth, and gain of 

 nitrogen. The subject in various aspects is being further 

 investigated at Eothamsted, and some of the results so far 

 obtained will be briefly referred to presently. 



