1918] AGRICULTUEAL BOTANY. 27 



witli each other and with other plant constituents. The presence of calcium 

 carbonate did not interfere with the humification of albumin and tannin. The 

 colorimetric method was found to be satisfactory for the determination of 

 humus. 



Humification of compounds entering into the composition of plants, A. G. 

 Tbusov {Selsk. Khoz. i Liesov., 252 (1916), Sept.-Oct., pp. 5-15). — Continuing 

 the above work, studies of the changes occurring in the composition of the 

 organic parts of decomposing birch leaves are reported. 



It was found that humus formation took place during the first brief period 

 of decomposition and that the humus consisted mainly of the surface parts. 

 Decomposition proceeded rapidly during the first 25 days, after which it pro- 

 ceeded more .slowly. The decrease of organic substances during the first brief 

 period of decomposition took place at the expense of the mineralization sub- 

 stances soluble in ether and alcohol. A certain decrease in the content of fats 

 and pentosans was noticed during decomposition, although no increase in 

 volume of humus resulted. 



It is concluded that the greater part of tannic substances contained in plant 

 residues decomposes very rapidly in from 8 to 12 days, this resulting in a pro- 

 portionate increase in water-soluble humus formation. 



Nitrog-en-assimilating organisms in manure, H. L. Fulmeb and E. B. Feed 

 {Jour. Bact., 2 {1911), No. 4, pp. 423-43^) .—Studies at the University of Wis- 

 consin on the nature of the organisms concerned with the fixation of nitrogen 

 in manures are reported. 



It was found that there are several groups of bacteria concerned with nitrogen 

 assimilation in manure. Bacterium azophile n. sp., which occurs abundantly in 

 fermenting manures, seemed to be the chief organism responsible for the in- 

 crease of nitrogen. The increase in nitrogen when the organism was gi-own in 

 a manure-extract medium amounted to from 3 to 5 mg. per 100 cc. of solution. 

 Twenty-eight degrees C. seemed to be a favorable temperature for the growth 

 of the nitrogen-assimilating organisms of manure. 



The relation of green manures to nitrogen fixation, H. L. Fulmeb {Soil 

 Sci., 4 {1917), No. 1, pp. 1-17, figs. 4)- — Investigations at the Wisconsin Experi- 

 ment Station on the relation of gi'een plant tissue to free-nitrogen-fixing organ- 

 isms in silt loam field soil and garden soil are reported. 



It was found that green manures, as clover, wheat, or oats, when added to 

 soil favored free nitrogen fixation. "A gain in nitrogen was noted in both soils. 

 The increase was highest with field soil, due perhaps to a greater number of 

 nitrogeu-fixiug organisms. A gain in nitrogen was observed (1) where green 

 tissue was applied to soil previously treated with a small amount of mannite, 

 (2) where treated soil was used to inoculate Ashby's solution, and (3) when a 

 pure culture of Azotobacter was used to inoculate a sterile solution containing 

 green tissue. The nonlegume tissue stimulated fixation more than the legume, 

 probably because of the nature of its carbohydrate content. 



" The results of these experiments in their entirety show that nitrogen fixa- 

 tion results from the addition of green manures to soil. . . . The plants giving 

 best results are the ones lowest in nitrogen content." 



Peculiar effects of barium, strontium, and cerium on Spirogyra, S. S. 

 Chien {Bot. Oaz., 63 {1917), No. 5, pp. 406-409, figs. 2).— Following up the in- 

 vestigations reported by Osterhout (E. S. R., 37, p. 130), the author has studied 

 a large form of the S. crassa type, also a smaller .species, in connection with 

 several salts. 



It was found that the cell chloroplasts of the larger species contract away 

 from the cell wall in a characteristic way in solutions of cerium trichlorid, 

 barium chlorid, and strontium chlorid, those of the smaller kind in the last two 



