1917] 
FREIBERG—MOSAIC DISEASES 183 
small section was not sufficient to give a noticeable reaction. 
From the tests on ferric iron it would appear that there 
is sufficient of this element present in all tissue to warrant 
the normal development of all cells. 
CALCIUM 
Calcium is generally detected as calcium sulphate. The 
sections were treated with a 3 per cent solution of sulphuric 
acid and allowed to stand until most of the solution had 
evaporated. Small plate-like crystals or needles of calcium 
sulphate were then noticeable in the remaining reagent, espe- 
cially along the edges of the sections and in the intercellular 
air-spaces. 
A second test applied was that with ammonium oxalate. 
The sections were treated with a 5 per cent solution of am- 
monium oxalate in а 10 per cent solution of acetic acid. The 
precipitate of calcium oxalate assumed the form of very 
small granules. The sections were tested further by adding 
a 9 per cent solution of oxalic acid containing a small amount 
of acetic acid. This gave satisfactory results, precipitating 
the calcium as minute crystals of calcium oxalate, pyramidal 
inform. The test was applied with equal success to all tissue. 
MAGNESIUM 
Besides being an indispensable element in the general nutri- 
tion of the plant, magnesium is important as an antidote for 
calcium and as a constituent of chlorophyll. Tests for mag- 
nesium were made by treating the sections with a 0.1 per 
cent solution of NaH(NH4)PO, and placing the slide in a 
moist chamber containing a vessel filled with strong ammonia. 
The ammonia vapor killed the tissue and rendered the cell 
easily permeable to the sodium ammonium phosphate. After 
several minutes, crystals of magnesium ammonium phosphate 
separated out. These were either short and triangular in 
form, or, depending upon the quantity of magnesium present 
and also upon the time for which the reagent was allowed to 
react, were x-shaped or stellate in form, the appendages as- 
suming a feather-like structure. 
