298 ANNUAL REPORT SMITHSONIAN INSTITUTION, 19 3 5 



of selenium on plants (Cameron, 1880) postulated that the injury 

 was due to substitution of selenium for sulphur in some essential 

 compound in the tissues. 



Regardless of the hypothesis to explain it, the tendency of an ex- 

 cess supply of sulphur to reduce the amount of selenium taken up by 

 plants may have some practical value. As a demonstration of this 

 possibility, I grew wheat plants in outdoor soil plots to which sele- 

 nium (as sodium selenate) was added at a rate of 2 parts of selenium 

 in a million of soil, mixed in to a depth of 6 inches. This is an 

 amount of selenium equal to the weight of about 20 grains of wheat 

 mixed into a soil mass weighing considerably over half a ton. Into 

 some of the plots was mixed ordinary flowers of sulphur at a rate 

 corresponding to three-fourths of a ton to the acre. When the grain 

 was ripe, its toxicity was tested by feeding it to white rats (Hurd- 

 Karrer and Kennedy). That from the plots receiving selenium alone 

 stunted the rats and produced the damaged liver typical of selenium 

 poisoning, whereas that from the plots that had received sulphur with 

 the selenium permitted normal growth and produced no detectable 

 symptoms of poisoning (pi. 6). Gypsum (calcium sulphate) was 

 similarly effective in rendering the grain nontoxic. 



Whether this effect of sulphur will supply the farmer with a prac- 

 tical means of con,trol or of amelioration of the disease caused by 

 selenium awaits testing under field conditions in the affected areas. 

 It is quite possible that the high cost of even the cheapest form of 

 sulphur may make the treatment of poorly productive land un- 

 feasible. 



One of the consequences of the theory that I have suggested to 

 explain the selenium-sulphur relationship is that the more sulphur 

 a plant normally requires in its metabolism, the more selenium it 

 will take in. It is well known that some types of plants require 

 more sulphur than others. Thus the plants of the mustard family, 

 such as cabbage, broccoli, kale, and cauliflower, utilize a great deal 

 to form the sulphur-containing compounds that give them their 

 characteristic tastes and odors. They use so much that the sulphur 

 of the soil must be replenished if such crops continue to be grown. 

 Plants of the grass family require very little, so that they can bo 

 grown year after year without producing a deficiency of sulphur 

 in the soil. It was therefore of both theoretical and practical in- 

 terest to find that when representatives of these groups were grown 

 in selenized soil, the selenium they took up paralleled their sulphur 

 absorption. In table 5 are reported a few of the data that have been 

 obtained showing this parallelism. The high sulphur absorption 

 of representatives of the Cruciferae (mustard family) is invariably 

 associated with a high selenium intake, and the lower sulphur ab- 



