790 The American Naturalist. [September, 
the root or its branches. Frank has found Rhizobia in stem, 
leaves and even the embryo. I have searched for them repeat- 
edly in tissues outside of the root but have not found any. 
Tubercles resemble growing tissues in the abundance of 
Albuminoid compounds. Calcium oxalate crystals are common 
in the noninfected cambium especially the cork phellogan. 
Some of the crystals have a coating of cellulose secreted around 
them by the cell protoplasm. Any abnormal growth resem- 
bles histologically the tissue upon which it develops; hence 
one would expect the tubercles to resemble anatomically the 
roots upon which they grow. Yet it seems that the tubercles 
have more anatomical characters belonging to a stem than to 
a root, as already indicated. 
RESUME. 
1. Root tubercles develop exogenously. 
2. Tubercles grow from a meristematic area surrounding the 
infected region and separating it from the external cork layer. 
3. Cork as well as e cue develop from a well marked 
phellogen. 
4. Tubercles have a well developed vascular system differ- 
ing from that of the root. 
5. Phaseolus vulgaris and Amphicarpaea comosa have tuber- 
cles with well developed lenticels, differing somewhat from 
those on the stem. . 
6. There is more or less starch in tubercles produced by 
Rhizobium mutabile. 
7. Sometimes Rhizobium mutabile contains highly refractive 
bodies whose nature is not definitely known. 
8. Anatomically a tubercle resembles a stem more closely 
than a root. 
9. Generally tubercles are not found empty at the close of 
vegetative period. 
10. Probably the plant does not reabsorb the protoplasmic 
contents of the Rhizobia at any time. 
‘11. Nuclei in tubercles of Phaseolus vulgaris undergo great 
changes. 
