610 Bottomley .— The Root-nodules of Ceanothus americanus. 
5. The Bacteria, when isolated and grown in pure culture, can fix 
free atmospheric nitrogen, and from their structure, mode of growth and 
formation of ‘ bacteroids 5 evidently belong to the Bacillus radicicola group. 
Literature cited. 
Atkinson, Geo. F. : The Genus Frankia in the United States. Bull. Torrey Bot. Club, vol. xix, 
No. 6, pp. 171-7, 1892. 
Beal, W. J. : Bot. Gaz., vol. xv, No. 9, p. 232, 1890. 
Bottomley, W. B. : The Root-nodules of Myrica Gale. Ann. of Bot., vol. xxvi, I9i2,pp. 111-17. 
Brunchorst, J. : Uber einige Wurzelanschwellungen. Unters. aus dem bot. Inst, zu Tubingen, 
Bd. ii, 1886. 
Hiltner, L. : Uber die Bedeutung der Wurzelknollchen von Alnus. Landw. Vers.-Stat., Bd. xlvi, 
1896. 
Kellerman, K. F.: Nitrogen-gathering Plants. Yearbook, Dept. Agric., U.S.A., 213-18, 1910. 
Spratt, E. R. : Morphology of Root-tubercles of Alnus and Elaeagnus. Ann. of Bob, vol. xxvi, 
pp. 119-28, 1912. 
EXPLANATION OF PLATE XXVIIL 
Fig. 1. Ceanothus velutinus. Root-nodules. Nat. size. 
Fig. 2. Ceanothus americanus. Root-nodules. Nat. size. 
Fig. 3. C. americanus. Transverse section of root-nodule, showing central stele and bacterial 
zone with radially elongated cells filled with Bacteria, x 50. 
Fig. 4. C. americanus. Longitudinal section of root-nodule, showing endogenous origin of 
branch, x 30. 
Fig. 5. C. atnericamis. Tangential section of root-nodule, showing the four zones, x 50. 
