1917] 
FREIBERG—MOSAIC DISEASES 179 
AMMONTA 
The presence of ammonia may best be determined by liber- 
ating the free gas by means of strong alkali, and collecting 
it with platinie chloride or Nessler's reagent. This can best 
be accomplished by placing a glass ring, the ends of which are 
smoothly ground, on a glass slide and placing in the center of 
the reservoir thus formed a drop of strong alkali. A drop 
of concentrated sodium hydroxide was used in the work re- 
ported here, and a narrow glass ring used for making hang- 
ing-drop cultures served to form the little compartment. The 
tissue to be tested was placed in the bottom of the compart- 
ment and enough sodium hydroxide was added adequately to 
cover the mount. After the addition of the alkali the com- 
partment was covered immediately with a cover glass, to the 
lower surface of which there adhered a drop of platinic 
chloride or a drop of Nessler’s reagent. 
When Nessler’s reagent was used, the drop assumed a deep 
yellow color which intensified, eventually resulting in the for- 
mation of a brown precipitate. In the case of platinie chlo- 
ride, characteristic octahedral crystals of ammonium platinie 
chloride separated out. The detection of ammonia in plant 
tissue has been attempted on the part of various workers by 
applying Nessler’s reagent directly to the sections. This 
test is, according to Molisch, unreliable, since various con- 
stituents of the tissue may not only change the color of the 
reagent to a yellow or brown, but a yellow color may be de- 
veloped when alkali alone is applied to the tissue. Volatiliza- 
tion of the ammonia in the manner described is therefore the 
only reliable method for its detection. 
When these tests were applied to the diseased leaves, splen- 
did results of equal intensity were obtained regardless of the 
kind of tissue used. It was therefore concluded that salts of 
ammonia might, as a source of nutrition, serve all cells to the 
same degree. 
TOTAL NITROGEN 
An unbalanced nitrogen relation between diseased and 
healthy tissues has been cited as a partial explanation of the 
cause of mosaic diseases (Woods, ’02). It therefore became 
