324 The Microscope. 



made out with a hand magnifier, the tissues, both of the leaves and 

 of the roots remain intact, until dead and dry, when the affected 

 parts soon crumble away. It seems to be only the exterior layer of 

 tissue or cortex of the roots in which the disease is resident. 



The injurious effects, now described have been attributed to 

 insects, and to parasitic fungi, to unfavorable conditions of soil and 

 of climate, and to constitutional weakness of the plants themselves. 

 The crops are not comparatively important ones in the country at 

 large, and are usually locally cultivated, so that relatively little 

 attention has been given to them by scientific investigators. But an 

 account of careful studies upon the diseased condition of the plants 

 and upon the insects infesting the fields is given in the Thirteenth 

 Report of the State Entomologist of Illinois (1883), by Professor 

 S. A. Forbes. These studies were avowedly unsatisfactory, but 

 finding great numbers of plant lice, of four distinct species, in the 

 fields, it was thought these, or some of them, probably caused the 

 mischief. If, however, the injury could be assigned to the lice at 

 all, Professor Forbes concluded that the main damage must have 

 been done before the time of his examination, and that the depredat- 

 ing insects had largely disappeared, for their distribution at the time 

 did not correspond with the evidence of damage done. He thought 

 the trouble might be due to fungi, and specimens were sent me for 

 examination, upon which a negative report was made. I am not 

 aware that the injury in question has elsewhere been attributed to 

 specified insects. 



In the Prairie Farmer for August, 1884 (Vol. Ivi., p. 532), I 

 gave a description of a fungus supposed to be an unnamed species of 

 Ghcetostroma found in abundance upon affected leaves of broom-corn. 

 This seemed, at the time, to cause at least some of the damage noted. 

 It has been found several times since, and probably does injure the 

 crop, but cannot be connected in anyway with the main disease with 

 which we are now concerned. 



This completed, so far as I am informed, the accounts that have 

 been published having reference to the particular and conspicuous 

 injury at present under discussion. If the references really are com- 

 plete, we can understand that very little has been known upon a 

 disease which has certainly existed at least six years in our country, 

 and which was probably imported from abroad with the affected 

 plants many years ago. 



