125 
A Inns and Elaeagnus . 
of cultivation, however, was to take a nodule, the outside of which had been 
sterilized, and cut it into three or four pieces, in order to expose] some 
of the cortical cells directly to the influence of external agencies, and then 
place them in liquid culture media and incubate them at 25 0 C. The 
media used were those described above for the cultivation of the isolated 
organisms. The influence of adding a trace of ammonium phosphate 
or asparagin was also investigated. The pieces of nodule were incubated 
for periods varying from 12 hours to 6 days, when they were removed from 
the culture medium, fixed in Bouin’s fixative, embedded and microtomed, 
and the sections stained with amyl gram or carbol fuchsin. In every case 
there was a steady increase from day to day in the proportion of bacilli 
present, and a corresponding decrease in the spherical bodies until after the 
fourth day, when all the latter forms had disappeared. The coccus forms 
were seen to divide, leaving a clear area across the centre, which always 
remained unstained (Fig. 14). Each half then divided again (Fig. 14), and 
the resulting bodies each produced a typical bacillus. In some cases there 
appeared to be more than four rod-shaped organisms produced from the 
one coccus, but the spherical body very soon loses its identity, especially 
when they are not too crowded together. All these stages are very 
evident in freshly gathered nodules, especially in the spring. These 
observations, like those in connexion with the isolated organisms, point to 
the conclusion that the amount of available carbohydrate present is one of 
the factors determining the production of the coccus form. It is extremely 
probable that the twining of the zoogloea round the nucleus of the host cell, 
as well as the activities of the Bacteria in these cells, impairs to a large 
extent the metabolic processes of the latter, and consequently renders 
it more difficult for the Bacteria to obtain the carbohydrate, their source of 
energy, and they consequently undergo a morphological change which 
renders them more resistant to the influence of their environment, and in 
this condition they rest. In the tubercles themselves, they become much 
more abundant in the autumn, in the winter appear to be the only form of 
organism present, and in the spring, when food material is once more avail- 
able and fresh cortical cells are being formed in the nodule, they divide 
and once more assume the active bacillus form. The greater resistant 
power of the cocci was illustrated by moving some of the pieces of tubercle 
which contained none of this form from one culture medium to another, 
when it was found that in 12 hours the formation of a large number had 
been induced by this sudden change in the constitution of the environment. 
The two forms are clearly polymorphic of the same organism, which is 
a species of P seudomonas radicicola . 
The tissue at the base of the tubercles contains an abundant supply of 
reserve food material, which consists mostly of oil, but in the spring a good 
deal of starch is present. In the older nodules this tissue becomes some- 
