ON THE NATURE OF MITOCHONDRIA 457 
in paraffin, they were cut into sections 3y in thickness, mounted, 
and stained with Bensley’s aniline fuchsin methyl green. 
The author has made no original observations on chloroplast 
formation. The work of Lewitsky, Regaud, Guilliermond, and 
other investigators in this field is accepted as fully demonstrated. 
Bacillus radicicola 
A longitudinal section of a root-nodule of the white clover, 
when examined with a low magnification of the microscope, 
reveals three distinct areas in the nodule. When a higher magni- 
fication is employed, the three distinct areas may be seen to be 
composed of cells containing three distinct types of bacteria- 
like organisms. Figures 1, 2, and 3 are camera-lucida drawings of 
portions of these three areas from a single nodule. 
In figure 1 the typical Bacillus radicicola may be recognized. 
Most of the organisms are rod-shaped. <A few of the characteris- 
tic Y-shaped individuals may be seen. It is this type, represented 
in figure 1, that, I believe, is generally considered the active in- 
dividuals in nitrogen fixation. They may be designated the 
‘mature forms.’ 
In figure 3 the cells contain small bodies that are not unlike 
mitochondria in appearance. These forms, undoubtedly, are 
the young bacilli that have recently entered the nodule, or 
they represent a young form that will later metamorphose into 
the mature type. They may be designated the ‘juvenile forms.’ 
Prazmowski (quoted by Marshall, ’12) and other investigators 
have demonstrated that the source of Bacillus radicicola is 
from the soil. The free-living forms are quite small. They 
enter the roots through the root-hairs. The host plant re- 
sponds with the production of the nodules into which the juvenile 
forms migrate and later metamorphose into the mature type. 
I have not been able to find a comprehensive description of the 
metamorphosis. 
In figure 2 the organisms found in the cytoplasm of the nodule 
cells are spherical in shape. I have been unable to find any 
mention of these forms in bacteriological literature. The Ameri- 
can text-books on bacteriology have no reference to them. 
They may be designated the ‘senile forms.’ 
