[Vor. 4 
182 ANNALS OF THE MISSOURI BOTANICAL GARDEN 
Tests were made for ferric iron by treating the section on 
the slide for an hour or more with a 2 per cent solution of 
potassium ferrocyanide and then adding a 5 per cent solu- 
tion of hydrochloric acid. In the presence of comparatively 
large amounts of iron, a deep blue (Berlin blue) color results. 
When only traces or minute quantities of iron are present, 
the reaction may be negative or a blue-green tinge developed. 
In this event it may be confused with the natural pigments 
and the results must be checked by more reliable methods. 
Fairly uniform results were obtained with the method de- 
scribed, but further evidence was secured in the following 
manner: The surfaces of well-mottled leaves were washed 
and rinsed with distilled water, thus removing all foreign 
matter, and the well-defined areas cut out by means of a 
sharp glass needle. These were then dried in an oven. Lack- 
ing a platinum plate, the samples were ignited on a glass plate 
and the above reagents applied. A marked reaction resulted. 
This method, furthermore, possessed the desirable feature 
that no metal instruments were used in handling the material. 
No serious error, however, should have been introduced by 
cutting the sections with a highly polished razor. 
The following test has been described for the detection of 
ferrous iron: The material is treated with a 2 per cent solu- 
tion of potassium ferrocyanide or potassium cyanide for an 
hour or more. A few drops of 5 per cent hydrochloric acid 
are then added. In the presence of ferrous iron a blue color 
(Turnbull blue) results. This test proved negative in both 
diseased and healthy tissue. 
When iron is present in organic combination it may be de- 
tected by incubating the material at about 60° C. with a solu- 
tion of ammonium sulphydrate and 50 per cent glycerin mixed 
in aliquot proportions. The sections were placed on the 
slide, the reagent applied, and covered with a cover glass. 
Upon the liberation of the combined iron, varying from a 
few days to a few weeks, a very dark green or almost black 
color signified the presence of ferrous sulphide. Uniform 
results were not obtained with this method, but this might be 
attributed to the fact that the amount of iron present in the 
