1917] 
FREIBERG—MOSAIC DISEASES 181 
minutes a violet color developed, indicating the presence of 
protein. This test is a comparatively difficult one. 
3. Xanthoproteie reaction: Strong nitric acid was applied 
to the material and the slide warmed gently over a micro- 
burner. А yellow color developed which changed to orange 
upon the application of strong ammonia. 
4. Iodine test: With iodine a deep yellow to brown color 
developed. 
In all of these tests a more pronounced reaction was ob- 
tained with the lighter or diseased areas than with the darker. 
In the former the color showed up somewhat faster and was 
more intense. We may not be justified, however, in assum- 
ing that there is actually a great deal more protein in the 
chlorotic area than in the other, since the values in all of this 
work are only relative in themselves, and the excess of carbo- 
hydrates, etc. present in the deep green areas may obscure 
the above reactions in part. We would, however, be safe in 
stating that there is as much protein in the lighter areas as 
in the darker, and that there is a probability of there being 
more in the former than in the latter. The validity of this 
statement can only be determined by accurate quantitative 
methods. 
It was originally intended to make analyses for amino 
nitrogen by the Van Slyke (713) method, but because of the 
need of choice material for other work reported here, this 
determination had to be deferred. 
IRON 
Iron is one of the elements absolutely indispensable for 
plants, and may be present in the tissue in either organic or 
inorganic combination. Since it is universally conceded that 
a lack of iron is directly responsible for a certain type of 
chlorosis or the inability of the plant to form chlorophyll, it 
was desired to show, if possible, whether there was any 
marked difference between the iron content of lighter and 
darker areas of diseased leaves. In making these tests, iron- 
free chemicals, glass needles, and a new highly polished razor 
were used, thus obviating all possible sources of error. 
