1921] SCHERTZ—MOTTLING 103 
per unit area from July 15 until November 5. Over three-fourths 
of the nitrogen disappeared in this time. 
In analyzing the leaves for total nitrogen when nitrates are 
present the method as described in Bulletin 107 (8) was used, 
with zinc as the reducing agent. Samples (10 gm.) of fresh leaves 
were ‘used, and the results were calculated to grams of nitrogen 
per too gm. of fresh leaves. This analysis gives the total of the 
three forms (31) of nitrogen which may be found in organic matter 
(such as leaves), namely, nitrogen in a state of organic combination, 
nitrogen in ammonia or its combinations, and nitrogen in a more 
highly oxidized state as salts of nitrous or nitric acid. Table XII 
shows that there is a marked reduction in the total nitrogen content 
of the leaf with mottling. Boncquet (5) found that the total 
TABLE XII 
PROTEIN NITROGEN-+NITRATE NITROGEN-+AMMONIUM SALTS 
Samp] Sam; Sampl pe al 
am oy a no. fT no. IIT Average | per roo gm. 
dry weight 
OG ea ee 0.283 0,267 0.249 0.266 4.19 
ween Ay O.1r7 0.107 0.103 0.109 1.87 
MO ee is 0.074 0.071 0.068 1.09 
nitrogen calculated on the basis of ash was always less in the 
diseased leaves than in the healthy ones. 
The amount of nitrogen present in the leaves as NO, was 
determined by the Schlésing-Wagner method as given in Bulletin 
107. For each determination 25 gm. of leaves was used. The 
leaves were finely ground in a mortar with quartz sand, boiled for 
2 hours, made up to a definite volume, filtered through cheesecloth, 
and the amount of nitrate estimated in an aliquot part. The 
amount of gas as nitric oxide set free was then measured in the 
burette of a Van Slyke apparatus (35), and the nitric oxide was 
absorbed in a Hempel pipette containing NaOH and KMn0,,. 
The residual gas was then measured in the burette. The difference 
gave the amount of nitric oxide, which was reduced to standard 
temperature and pressure, and was calculated to grams of nitrogen 
per 100 gm. of wet weight, as given in table XIII, which shows an 
