[51] Hilgard and Jaffa. On the Nitrogen-content of Soil-humus in the Humid and Arid regions. Rep. Cal. Exp’t Station for 1892-4; Agric. Science, April, 1894; Wollny’s Forsch. Geb. Agr. Phys., 1894.
[52] Introduced only for comparison of the nitrogen percentage in Humus and not included in the average.
[53] Bull. No. 53, Minn. Exp’t Station, p. 12, Chem. of Soils and Fertilizers, p. 94.
[54] The figures for cow manure are so far out of range with any others thus far observed, that it seems reasonable to suppose that they are influenced by unchanged substances present in the excreta.
[55] Bull., S. Dakota Station, Nos. 24-32, 35, 47.
[56] The mode of statement in the paper is not always quite clear as to the manner in which the averages given were calculated. It must be remembered that these data refer to cubic centimeters of soil, or about twice the amount (1 gram) used by European observers.
[57] Uber die Pilzsymbcose der Leguminosen, Berlin, 1890.
[58] Original figure from drawing by O. Butler, Asst. in Agr. Dep’t Univ. of California.
[59] “Living together” beneficially; in contradistinction to parasitism, which is injurious to the host plant.
[60] It is asserted by some observers that the root-bacilli producing differently-shaped excrescences upon different legumes are distinct species; but this view is not sustained by the experiments of Nobbe and Hiltner, and seems intrinsically improbable.