1917] 
FREIBERG— MOSAIC DISEASES 185 
A second test described for the detection of phosphorus is 
its precipitation as ammonium magnesium phosphate. The 
solution used for the determination consists of 25 volumes of 
a saturated aqueous solution of magnesium sulphate, 2 
volumes of a saturated aqueous solution of ammonium 
chloride, and 15 volumes of water. This solution when ap- 
plied to salts of phosphorus yields crystals of ammonium 
magnesium phosphate such as were described above under 
magnesium. 
The writer was unable to get uniform results with either 
of these tests, regardless of the kind of tissue to which they 
were applied. When samples of diseased and healthy tissue 
were ignited a faint indication of the presence of crystals 
was detected at intervals in the residue, but the results on the 
whole were not encouraging. Because of the fact that this 
was experienced with healthy and normal tissue to the same 
degree as with diseased tissue, we may be justified in con- 
cluding that the disorder cannot be attributed to a marked 
unbalanced phosphorus relation. 
SULPHUR 
Sulphur is absolutely essential for plant growth, usually 
being present in organic combination. When present in in- 
organic form it may be detected as calcium sulphate by means 
of calcium acetate, or as lead sulphate with lead acetate, or 
as barium sulphate with barium chloride. Organic sulphur 
can best be detected after its liberation by ignition of the 
tissue. 
The tests for sulphur gave results much the same as those 
for phosphorus. It was difficult to demonstrate its presence 
even in normal healthy tissue, and we are therefore unable 
to correlate any metabolic disturbance with a lack or a super- 
abundance of this element. 
TESTS FOR CARBOHYDRATES 
From the marked difference in chlorophyll content of the 
lighter and darker areas of diseased leaves, it seemed self- 
evident that there must be a great difference in the carbo- 
