ASPECTS OF AN OLD AGRICULTURAL QUESTION. 271 



(22) The literature of the whole subject up to 1894 has been very 



thoroughly gathered together by MacDougal in Minnesota 

 Botanical Studies, Geo/, and Nat. Hist. Survey of Minnesota, 

 bull. No. 9, part iv., Minneapolis, Sept., 1894. 



(23) Hellriegel and Wilfarth. Zeitschr. f Rubenzucker In- 



dustrie, Nov., 1888, and Bericht., Wien, 1890. (See also ref. 

 22.) 



(24) Laurent and Schloesing. Recherche sur la fixation de 



l'azote libre par les plantes. Ann. Inst. Past., 1892. (See 

 also ref. 22.) 



(25) FRANK. The best account of Frank's results is given in his 



Lehrbuch der Botanik, 1892, b. i., pp. 574-584, with his own 

 selection from the literature. 



(26) KOSSOWITSCH. Durch welche organe nehmen. de Leg. den 



freien Stickstoff auf. Bot. Zeit., 1892. 



(27) Beyerinck. Bot. Zeit., 1890. 



(28) Frank. Ber. d. deutsch bot. Gesellsch., 1889. 



(29) KOSSOWITSCH. Bot. Zeit., 1894, h. 5., p. 97. 



(30) DUCLAUX. Ann. Inst. Past., 1894, p. 728. 



(31) LlEBlG. Chem. of Agri. and Phys. My edition is the third, 



1843, p. 23. 



(32) Frank. Lehrbuch, vol. i., p. 583. 



(33) MACDONALD and Kellas. Paper read to Roy. Soc, Mar. 



21, 1895. (See Nature, 1895, p. 620.) 



H. Marshall Ward. 



