The Root-nodules of Ceanothus americanus. 
BY 
Professor W. B. BOTTOMLEY. 
With Plate XXVIII. 
A S far as can be ascertained, Dr. W. J. Beal of the Agricultural College, 
l Michigan, U.S.A., was the first to call attention to the tubercles 
occurring on the roots of Ceanothus. At the meeting of the American 
Association for the advancement of Science held at Indianapolis in 1890 he 
exhibited specimens of what he called ‘ root-galls ’ on the larger roots 
of Ceanothus americanus. 
Two years later Atkinson described the structure of these root-galls 
and stated that the gall is inhabited by a fungus which 4 when mature 
forms compact botryoid clusters in the affected parenchymatous cells of 
the gall, the central portion being composed of a complexly-branched 
mass of threads bearing at their ends on the periphery of the mass the 
globose sporangia’. He considered the fungus to be related to the genus 
Frankia of Brunchorst, and proposed for it the name Frankia Ceanothi. 
No further mention of these structures can be found until 1910, when 
Kellerman, in a paper on ‘Nitrogen Gathering Plants’, states that ‘nitrogen 
fixing Bacteria, apparently similar to the Bacteria isolated from the 
Leguminosae, have been isolated from nodules of Ceanothus\ Unfor¬ 
tunately he gives neither references to any research work nor experi¬ 
mental evidence in support of his statements. Kellerman’s paper is 
illustrated by photographs of root-nodules from a number of non-legu- 
minous plants, and on examining these one is struck by the remarkable 
resemblance between the nodules of Alnus , Elaeagnus , and Ceanothus . 
As Hiltner had demonstrated in 1896 that the root-nodules of Alnus 
and Elaeagnus are concerned with nitrogen assimilation, the resemblance 
suggested the possibility of the root-nodules of Ceanothus having a similar 
physiological significance. 
There was a difficulty at first in obtaining material for investigation. 
An examination of the roots of Ceanothus plants growing at Kew Gardens, 
Chelsea Physic Gardens, and various nurseries and private gardens failed 
to reveal a single nodule. The foreman gardener of one large nursery 
[Annals of Botany, Vol. XXIX. No. CXVI. October, 1915.] 
