ARTICLE V. The Helminthosporium Foot-rot of Wheat, with Observations 

 on the Morphology of Helminthosporium and on the Occurrence of Saltation in 

 the Genus. By F. L. STEVENS. 



INTRODUCTCXRIT / , -,^ 



The present study of wheat disease is^baseti upon Vfo6t-fot/6r rot of 

 the basal portion of the stems, of wheat plants, as it occurred in Madison 

 county, Illinois, in 1919 and subsequently. This disease was first reported 

 in United States Government publications as " take-all" ( Ophiobolus gram- 

 inis] ; later, merely as "take-all," no cause being assigned; and for some time 

 past, in Government publications it has usually been designated as "so- 

 called take-all." An annotated bibliography of nearly one hundred 

 titles concerning foot-rot disease of wheat, prepared by the writer, was 

 presented before the Cereal Pathologists of America at St. Louis in June, 

 1919, and this, expanded to one hundred and eighty-eight titles, was 

 published in October, 1919 (116). As early as May, 1919, cultural studies 

 quite clearly pointed to Helminthosporium as the true cause of the disease, 

 and at the December meeting of the American Phytopathological Society 

 I announced this fungus as the probable cause. In May, 1920, in a note in 

 Science (117), I published the statement that it had been conclusively 

 established that this foot-rot of wheat is caused by Helminthosporium. 

 One purpose of the present paper is to present the evidence on which 

 the foregoing conclusion is based and certain facts concerning the mor- 

 phology and parasitism of the fungus; but far transcending in interest the 

 disease itself which now appears to be one of much less alarming nature 

 than was at first feared is the fact that very striking phenomena of 

 variability are found in this and related fungi. In the following pages, 

 therefore, appear (I) an account of the Illinois foot-rot of wheat and its 

 causal fungus; and (II) evidence and discussion of the occurrence*of salta- 

 tion within the genus Helminthosporium. 



ACKNOWLEDGMENTS 



In this study I have been assisted financially by grants from the 

 Illinois Natural History Survey and from the University of Illinois. I 

 am indebted for specimens to persons mentioned in the list of species 

 used for comparison (pages 181-184), and to W. P. Snyder for compu- 

 tation of data embodied in several of the graphs. I wish also to express 

 my thanks to Prof. J. A. Detlefsen, who kindly read the manuscript and 

 offered valuable suggestions regarding genetic questions. 



