1917] 
FREIBERG—MOSAIC DISEASES 189 
a line of experimentation which seemed more fundamental. 
The tests described above were carried out on diseased and 
healthy tobacco plants. The results are primarily relative, 
yet the relativity is to a certain degree quantitative, and 
enough so to justify us in concluding that calcium and nitro- 
gen may be more abundant in the chlorotic areas, while car- 
bohydrates are more plentiful in the green tissue. The cause 
of this unbalanced condition is not apparent at present. It 
is essential, however, that all these observations be substan- 
tiated by reliable quantitative analyses. 
PHYSIOLOGICAL RELATIONS 
From the results reported above, and especially those re- 
lating to the inorganic constituents of the tissue, it is very 
evident that the real cause of the disease is more deeply seated 
than has been intimated in some literature on mosaic diseases. 
There is therefore reason to believe that the cause, if not 
associated with parasites, is essentially organic in nature, as 
is suggested by the work of Woods (’02) and others. 
Woods (’02) maintained that mosaic diseases could be 
attributed to an excess of oxidases, since a more pronounced 
oxidase reaction was evidenced by diseased plants, and also 
when ridding his extract of oxidases, he lost the infective 
mosaic principle. However, this may not be the right inter- 
pretation, and to the writer this increase in oxidase reaction 
seemed to be an effect and not a cause of the disease. We 
would not conclude that the diminished sugar content of the 
lighter areas of the tissue as compared with that in the darker 
areas is responsible for the disease, but rather that this, as 
also the difference in oxidase activity, is in reality only the 
result of the disorder. 
The writer therefore undertook to eliminate the oxidases 
from extracts of diseased plants without destroying their in- 
fectious properties, or, if it were possible, to secure a solution 
which from the start possessed infectious properties but no 
oxidase activity. Since Allard (714, 715) has shown that the 
infective principle may be obtained from all parts of the plant 
