[Vor. 4 
178 ANNALS OF THE MISSOURI BOTANICAL GARDEN 
event, the reaction may be intensified by using thicker sec- 
tions and a more concentrated solution of the reagent. 
This reaction does not enable us to distinguish between 
nitrites and nitrates, but the former group of compounds has 
never been demonstrated in normal green tissues (Klein, 713) 
except in one plant, namely, Erythrina coralloides (Wee- 
huizen, 09). Тһе test employed by Weehuizen was as fol- 
lows: The freshly expressed juice was tested with potassium 
iodide starch-paper. In the presence of nitrites a blue color 
developed which did not disappear upon treatment with sul- 
phanilie acid and dilute sulphuric acid, but did turn to a саг- 
mine red upon the application of an alcoholic solution of 
alpha-naphthylamine. In adapting the test to the micro- 
chemical work, the potassium iodide starch-paper was made 
by soaking filter paper in a mixture of 50 ce. of 1 per cent 
starch paste and 50 сс. of 3 per cent potassium iodide solu- 
tion. A 0.1 per cent solution of alpha-naphthylamine was 
employed. Negative results were obtained when this test 
was applied to the juice expressed from diseased tobacco 
leaves. 
Reaction with brucine.—Another test for inorganic nitro- 
gen, though less delicate than that of diphenylamine, is the 
one with brucine. The reagent is applied as 0.2 gram brucine 
in 10 сс. reagent sulphuric acid. In the presence of nitrogen 
a deep red color is produced. In the presence of small quan- 
tities of nitrogen this test may fail completely, though re- 
sults may have been obtained with diphenylamine. 
When applying these tests to diseased tobacco tissue, fairly 
uniform results were obtained with diphenylamine. With 
brucine, however, the results were less satisfactory, being en- 
tirely negative or comparatively faint. This was true regard- 
less of the kind of tissue examined, whether from the darker 
or the lighter areas. The results with diphenylamine, how- 
ever, led the writer to conclude that not only is nitrogen 
present in both the lighter and darker areas, but that it is 
present in about the same quantity in both types of tissue. 
