A Comparative Account of the Root-nodules of 
the Leguminosae. 
BY 
ETHEL R. SPRATT, D.Sc., A.K.C., 
University of London, King s College , and Battersea Polytechnic. 
With PJate XIII and five Figures in the Text. 
In the Text-figures m. — meristematic zone ; B. = bacteroidal tissue ; c. = outer protective cells ; 
v.b. — vascular strand ; r. = root. 
P LANTS which are capable of producing root-nodules when Bacillus 
radicicola penetrates into the root-hairs and subsequently the cortical 
cells of the root may be placed in two classes — those which belong to the 
Natural Order Leguminosae and those which do not. All these structures 
have been shown by several investigators to be actively concerned with 
assimilation of nitrogen. The bacteria utilize the free nitrogen of the 
atmosphere, and since the plants associated with them can live in very poor 
soil they produce nitrogenous material which can be assimilated by the 
plant. 
This symbiotic association is characteristic of the two gymnospermous 
families Cycadaceae and Podocarpaceae, the dicotyledonous families 
Elaeagnaceae and Myricaceae, and the genera Alnus and Ceanothus . 
Although these plants are widely separated in any other classificatory 
scheme, they are all non-legumes producing root-nodules containing Bacillus 
radicicola *. Each of these nodules has individual characteristics, but in 
every case the bacteria penetrate the root-hair and enter the cortex of the 
root without causing any morphological change, until a young lateral root 
during its passage through the cortex of the parent root becomes infected, 
when its development is so altered that it becomes a nodule. The plerome 
was already differentiated when the bacteria entered, therefore they 
attacked the cortical cells only, the stele retaining its central position and 
the growing point remaining apical (see Text-fig. i). 
The nodules which are characteristic of the Leguminosae are produced 
by infection of the root-hairs and cortex by the same organism, which here 
stimulates the cortical cells to increase in size, thus producing a local swell- 
ing which very soon becomes visible (see PL XIII, Fig. 6). A basal meristem 
[Annals of Botany, Vol. XXXIII. No. CXXX. April, 1919.] 
