198 ANNUAL KKFORTS OF KEl'ARTMENT OF AGRICULTURE. 



many cases entirely wortliless or even harmful. In some cases these 

 have been tested in the liehl, but mere laboratory and Greenhouse 

 examinations will often <j:ive an indication of their comparative 

 values. In this way attention has been directed to the utilization of 

 some valuable materials, and on the other hand both farmer and 

 manufacturer have been si)ared the loss of money or crops by the 

 use of materials of doubtful value. 



PLANT DISEASES. 



ROTS OF CORN AND SCAB OF WHEAT AND OTHER CEREALS. 



ROTS OK CORN ROOTS, STALKS, ANU KAUS. 



Losses in the United States in 1919 from this grou]) of corn dis- 

 eases are conservatively estimated at 125,175,000 bushels, or about 4 

 per cent. Research on these diseases, in cooperation with the Indiana 

 and Wisconsin Agricultural Experiment Stations and other agencies, 

 has been directed chiefly along four lines: (1) The symptoms of the 

 diseases, (2) relation of the condition of the corn plant to suscepti- 

 bility, (3) effects of the diseases on the physiology of the plant, and 

 (4) control measures. 



Symjytoms of the (nseases. — The results in the past year have veri- 

 fied those of previous years by showing that the diseases reduce yields 

 either by killing or lowering the vitality of kernels and seedlings, 

 thus causing poor stands; also by causing barren stalks, leaning or 

 broken stalks, and broken ear shanks. 



ReJation of the condition of the corn 2)lant to susceptibility . — Imma- 

 ture or starchy seeds produce plants that are more susceptible to the 

 attacks of these diseases than are those from seed well matured and 

 horny. The immature and starchy ears usually haA'e a much rougher 

 denting than the well-matured horny kerneled ears. This discovery 

 is unusually important, as by physical selection alone it is possible to 

 discard a high percentage of the seed ears that would produce plants 

 more susceptible to the disease. 



Investigations show also that various unfavorable soil conditions 

 either may produce plants having appearances very similar to dis- 

 eased plants or may predispose fairly health}' plants to attacks of 

 the diseases. An acid soil reaction seems to be associated with such 

 predisposition to disease. 



Effects of the diseases on the physiology of the host. — The researches 

 indicate that the nutrition of a diseased plant is abnormal. Chemical 

 analyses show that infected and disease-free plants vary in composi- 

 tion. Diseased plants often show, in and near the nodes, deposits of 

 harmful substances which interfere with the normal functioning of 

 those structures. 



Control 77ieasures. — A convenient method of testing seed corn for 

 germination and disease infection has been devised. The ordinary 

 rag-doll germinator has been modified by combining with it an 

 insulating sheet of heavy glazed paper. When the rag doll is rolled, 

 this paper lies between the successive layers of cloth carrjnng the 

 kernels and so prevents the growth of the rots and molds through the 

 cloth. This confines the infection, in a large measure, to the kernels 

 already infected and permits the certain identification of sound ears. 



