606 Bottomley .— The Root-nodules of Ceanothus americanus . 
stated that during his fourteen years’ experience of cultivating Ceanothus , 
both the deciduous forms belonging to the C. azureus group and the 
small-leaved varieties such as C.dentatus and C.floribundus , he had never seen 
a root-nodule in any Ceanothus plant similar to those he was familiar with 
on Elaeagnus roots. This is perhaps not surprising when one remembers 
that Ceanothus is an imported plant, and presumably the soil is devoid 
of the requisite nodule-forming Bacteria. A similar case is known in Soja 
bean plants grown in this country, which fail to produce root-nodules unless 
inoculated with the specific organism from abroad. 
Eventually a plentiful supply of root-nodules was obtained from 
Ceanothus plants growing wild in North America, where the genus is 
indigenous, through the kindness of Dr. Kellerman of the United States 
Department of Agriculture and Professor F. Clements of the University of 
Minneapolis. 
Nodule-bearing roots of two different species were received— Ceanothus 
americanus (New Jersey tea) and Ceanothus velutinus (mountain balm). 
As a preliminary examination showed that the nodules of both species are 
practically identical, the following description of C. americanus applies 
equally to C. velutinus. 
External Structure of the Nodule. 
The nodules when young are flesh-coloured, cylindrical outgrowths, 
from 3 to 8 mm. in length by i to z. mm. broad. They are first visible as 
tiny lateral swellings on the young roots, and soon attain a breadth of 
i to z mm., after which growth is confined to the apex until a length of 6 to 
8 mm. is reached. This concludes the growth for the first year. In the 
following year they continue their growth by branching near the apex, pro¬ 
ducing two to five branches, and each branch repeats the growth of the 
primary nodule. This branching is continued in successive years, each 
year’s growth remaining from i to z mm. in diameter and 4 to 6 mm. 
in length. Thus the nodules are perennial, and after a few years there 
is formed a loosely-branched, rotund mass, the size of a small walnut. The 
number of branches arising each year is variable, two, three, four, or even 
five branches being produced near together. Hence there is a greater 
diversity of branching in Ceanothus nodules than in other non-leguminous 
nodules where bi- or trifurcation is characteristic. 
Internal Morphology. 
The material used for the purpose of investigating the internal structure 
of the nodules was fixed in either Bouin’s fixative or alcohol, and micro- 
tomed sections were stained with Flemming’s triple stain, Heidenhain’s 
iron-haematoxylin, or Kiskalt’s amyl gram. A transverse section through 
