292 ANNUAL REPORT SMITHSONIAN INSTITUTION, 19 3 5 



In order to see how much selenium is necessary to visibly injure 

 wheat plants I set up a series of experiments with increasing amounts 

 of selenium in the form of sodium selenate added to pots of soil in 

 the greenhouse. When the concentration reached 15 parts of sele- 

 nium in a million of soil — i. e., 15 times the amount used to produce 

 the grain that was toxic to rats — snow-white areas or streaks ap- 

 peared on the leaves, like those on barley described by Turina (1922). 

 With more selenium in the soil the entire leaf was sometimes snow- 

 white. Such " chlorotic " plants look much like the decorative rib- 

 bon grass of the flower garden (pi. 2). 



Under some conditions a still more striking sign of injury ap- 

 peared, viz, the white areas became a beautiful deep rose or lavender- 

 pink. This color is quite unlike the effect of any other known 

 poison. 



With some types of selenium salts, namely, the selenites, the roots 

 become reddish, suggesting the presence of precipitated selenium. On 

 examination with the microscope, the pink root tissues are seen to 

 contain myriads of tiny red granules of selenium. This process of 

 "■ reduction " of the colorless selenium salt to the colored element 

 within the cell (Levine, 1915; Stoklasa, 1922; Turina, 1922) is a 

 unique source of color in plants, the usual colors of leaves and 

 flowers being due to organic pigments synthesized by the leaves. The 

 red selenium color has been put to practical use in making red glass, 

 such as that used for signal lights in railroad and traffic control, 

 and the red enamels used in ceramics. 



Chemical analyses show that selenium accumulates in plants in 

 such quantities that its concentration becomes much higher than in 

 the soil (table 1). In other words, the roots keep absorbing it and 

 passing it on to the leaves, where it accumulates and makes the plants 

 poisonous to animals. Up to a certain amount, about 300 parts per 

 million, or 0.03 percent, of the dry weight, it does not affect the 

 appearance of the wheat plant. But with larger amounts the char- 

 acteristic " chlorosis " of the leaves appears. Wheat plants are 

 almost killed by an accumulation of selenium equal to about one- 

 tenth of 1 percent of the solid material of the leaves. Some other 

 kinds of j)lants take up much more than this without showing injury, 

 notably crops of the mustard family (table 2). Certain wild plants 

 of the Wyoming seleniferous soils are reported to have a selenium 

 content equal to nine-tenths of 1 percent of their dry weight (Byers). 

 Naturally, such vegetation is extremely toxic to animals, and is now 

 suspected to be the cause of a livestock disease of that area known as 

 " blind staggers " (Beath, Draize, Eppson, et al., 1934; Beath, Draize, 

 and Gilbert, 1934; Draize and Beath, 1935). 



