94 BOTANICAL GAZETTE [FEBRUARY 
veins still showed a greenish tint some nitrates were found to be 
present. The last traces of nitrate in the leaf were found only in 
the petioles. In a moderately yellowed plant whose leaves were 
very slightly green, nitrates were found only in the pith region 
at the base of the stem; hence nitrates began to disappear at the 
very tip of the leaves and were last found only at the base of the 
stem. The nitrates disappeared last in the storage regions. 
Among other workers in microchemistry, Swart (48) found 
that in yellow leaves in autumn the amount of phosphorus, nitrogen, 
-and potassium decreased shortly before the leaves fell. Comparing 
this with the mosaic disease of tobacco, FREIBERG (18) reports 
that more proteins were present in the lighter areas of the leaves 
than in the darker. Nitrates were present in about the same 
quantities in healthy and diseased areas. Ammonium salts, iron, 
calcium, magnesium, potassium, phosphorus, and sulphur were 
also present in the same quantities in the chlorotic and in the dark 
green areas. By employing Folin’s micro-Kjeldahl method less 
nitrogen was found in the dark areas than in the lighter diseased 
areas. Diseased areas of the tobacco leaf gave a more pronounced 
reaction with Millon’s reagent, the xanthoproteic reaction, and the 
biuret test than did the healthy areas. More carbohydrates were 
always present in the dark green or healthy areas. 
Macrochemical analysis 
Since the whole leaf of the plant mottled completely, it was 
easy to compare the green with the mottled leaves by an analysis 
of the leaves, including the petioles, for the presence or absence of 
the substances which were suspected of causing the disturbance. 
In making the following analyses, controls were always run on a 
known sample, and in many cases several methods of analysis 
were tried and the one which gave the best theoretical results 
was used. 
In estimating the amount of iron present in the leaves, the 
method described by Marriott and Wo.rF (34) was used. The 
blade, petioles, and region of the abscission layer were analyzed 
separately. A piece 3-4mm. long was used for the analysis of 
iron in the abscission layer, and the petiole was cut off at the base 
