1914] KELLEY—FUNCTION OF MANGANESE 217 
Experimental observations 
The macroscopic appearance of a number of plants when 
grown on manganiferous soil is characteristic. Pineapples develop 
chlorosis at an early age, from which they never recover. The 
effects are first noticeable by a yellowing on the margins of the 
leaves or the development of yellow spots which soon spread over 
the entire leaf. The growing tips die back, the leaf margins 
becoming brown. Usually such plants produce small fruit of an 
abnormally pink color. Pineapple roots, instead of maintaining 
the usual pointed growing tip, are often found to be greatly enlarged, 
sometimes to the size of a lead pencil. The roots of other plants 
also become modified to some extent. Those of Panicum molle 
are found to be abnormally woody. Others are similarly affected. 
Corn makes poor growth, the leaves turning brown at an early 
Stage and the stalks taking on a deep purple color. Barley, oats, 
and rice are likewise stunted in growth. Of the Leguminosae, the 
cowpea (Vigna catjang), in particular, is very sensitive to man- 
anese; the lower leaves become brown, die back from the tips, 
and fallaway. The pigeon pea (Cajanus indicus) is affected some- 
what similarly. Onions also die back from the tips and produce 
very small bulbs. 
Some species, however, appear not to be affected. The Agave 
sisalana shows no effects; sugar cane is not greatly affected, and 
cotton and tobacco, although somewhat retarded in growth, are 
hot otherwise affected. Waltheria americana, the sow thistle, and 
@ species of Crotalaria grow as weeds on the manganiferous soils 
and are in no way hindered in their development. These illus- 
trations could be greatly enlarged, but are sufficient to indicate 
that the apparent effects of manganese in different species are far 
from being uniform. 
Microscopicat stupirs.—From a microscopical study of the 
Several parts of these plants, it was found that in those instances 
where manganese exerts a toxic effect, the cell walls of the root 
cortex become brown, and in some instances contain minute gran- 
ules of manganese dioxide. In a few instances the cells having 
brown cell walls extend into the central cylinder of the root, and 
