196 Symptoms of Poisoning in Plants [3894 
and Vicia faba as well as to Pelargonium. The first ten 
elements (arsenic, boron, copper, manganese, zinc, lead, mer- 
cury, iodine, chromium, and barium) were applied also to 
Chrysanthemum frutecens, Bryophyllum calycinum and 
castor bean (Ricinis communis). Except as noted, all appli- 
cations were in the concentration of 500 parts of the poison- 
ous element per million parts of soil. In order to avoid local 
injuries to the stem large applications were frequently divided 
and added in several portions at intervals of a few days. 
The following elements gave no determinable poisonous 
effects on any plant, in the concentrations used: arsenic, 
barium, bromine, cobalt, copper, lead, manganese, nickel, 
silver, uranium, vanadium and zinc. A slight improvement 
of color and general condition was noticed in Pelargonium 
with manganese and zinc. There was also a slight, but un- 
mistakable, stimulation of the growth of this plant by arsenic 
in the higher concentrations but this conceivably may have 
been due to some chemical action in making more available 
the phosphorus or other nutrients in the soil. 
Pronounced toxic effects were observed with boron, chro- 
mium, iodine, lithium and mercury, and it is interesting 
that these effects were largely so specific as to permit imme- 
diate recognition of the particular poison by mere inspection 
of the plant. Thus on Pelargonium the effect of boron is the 
development of dark-green areas, 1 to 5 mm. wide, inward 
from the edges of the leaves. This altered strip gradually 
dries and hardens, without becoming brown, and the leaf 
falls after from one to four weeks. The dark-green coloration 
does not extend to the whole leaf. Lithium shows a some- 
what similar behavior, but the altered area on the edge of the 
leaf is wider and is a light gray-green instead of dark green. 
It shows a very characteristic banding of the color in narrow 
light and dark lines parallel to the leaf edge. With iodine 
the leaves turn yellow on the edges and this yellowing gradu- 
ally extends inward over the whole leaf. Not until the leaf 
has turned entirely yellow does it fall or wilt appreciably. 
Mercury produces a somewhat similar yellowing of the leaves, 
