The Morphology of the Root Tubercles of Alnus and 
Elaeagnus, and the Polymorphism of the Organism 
causing their Formation. 
BY 
ETHEL ROSE SPRATT, B.Sc., A.K.C. 
Demonstrator in Botany at King's College , London. 
With Plates XIII and XIV. 
A MONGST the earlier investigators in the domain of the utilization 
of atmospheric nitrogen by plants, Hiltner stands out prominently, 
and in his work of 1899 the roots of Alnus and Elaeagnus , two non- 
leguminous plants, were shown to possess root tubercles which were 
associated with the assimilation of atmospheric nitrogen. These observa- 
tions have been amplified more recently by Bottomley, who isolated 
a bacillus from the internal tissue of these nodules, and with a pure culture 
of this organism inoculated some Vicia sativa seedlings, upon the roots of 
which characteristic tubercles containing P seudomonas radicicola were 
subsequently produced. From this experiment it was inferred that the 
tubercles of Alnus and Elaeagnus contained Pseudomonas radicicola , and 
infection of the roots by this organism was regarded as the probable cause 
of their formation. The literature concerning the tubercles of both these 
plants has greatly increased during recent years, and the various authors all 
find within the nodules a spore-producing hyphal-fungus, which has been 
placed in the group Hyphomycetes, but they do not appear to agree with 
one another in the detailed structure of this parasite, and its effect upon the 
host plant. The present communication is an account of some investiga- 
tions which entirely support the original view, put forward by Hiltner and 
upheld by Bottomley, that there is a symbiotic relationship between these 
two plants and the organisms causing the tubercle formation. 
Nodules have been obtained, at various seasons of the year, from plants 
of Alnus incana , Elaeagnus edulis , and Elaeagnus rhamnoides , growing at 
Chelsea, Sevenoaks, and North Wales. The material used for sectioniz- 
ing was fixed in either Flemming’s or Bouin’s fixative or absolute alcohol, 
the latter having the advantage that only in this case is the oil which 
is present in large quantities in the tubercles of Elaeagnus removed by 
[Annals of Botany, Vol. XXVI. No. CI. January, 1912.] 
