196 Symptoms of Poisoning in Plants [394 



and View 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, 



