The Root-Nodules of the Cycadaceae, 
BY 
ETHEL ROSE SPRATT, D.Sc., A.K.C. 
University of London, Kings College. 
With Plate XXIX. 
HE Cycadaceae are a group of special interest, owing to their retention 
i- of a greater number of primitive characters than are possessed by any 
other living group of Gymnosperms. Representatives of this group probably 
existed during the Mesozoic Period and were very widely distributed. The 
living cycads are represented by five eastern genera: Cycas , Encephalartos , 
S tang evict, Macrozamia , and Bowenia , and four belonging to the western 
hemisphere: Zamia , Microcycas , Dioon , and Ceratozamia , all of which are 
tropical or subtropical. In all the genera with the exception of the mono¬ 
type genus Microcycas , which is confined to Cuba, and has not been 
examined by the author, there are in addition to the primary tap-root 
numerous small secondary roots, some of which form the so-called root- 
nodules. 
These structures have been described as ‘ Coralline roots * in Cycas , 
where they occur abundantly immediately below the surface of the soil and 
protruding above it. Reinke described them as special organs for aeration, 
Schneider suggested a symbiotic association, and Life isolated from them an 
Alga and some Bacteria, and believed them to be concerned in the assimila¬ 
tion of nitrogen as well as aeration. More recently Zach states that they 
are not symbiotic, but contain a fungal parasite against which the cells react 
as a phagocyte. 
Amongst non-leguminous plants it is now recognized that the Elaeagna- 
ceae, Myricaceae, Podocarpineae, and the genus Ahius have root-nodules, 
which are definitely concerned with nitrogen assimilation. With these the 
Cycadaceae must be associated, because Bottomley has isolated from the 
nodules of Cycas not only Bacillus radicicola but also Azotobacter , both 
of which organisms are known to assimilate atmospheric nitrogen. They 
are, however, of special interest because in their cortex a very definite green 
ring, the algal zone, is produced by the presence of an Anabaena , which has 
been described by the author. 
[Annals of Botany, Vol. XXIX. No. CXVI. October, 1915.] 
