GRASSES OP IOWA. 267 



refer to this disease, but on some varieties cf corn it is very- 

 severe 



We have seen this fungus so abundant as to seriously destroy 

 the leaves and sheaths of corn, in fact so abundant as to mate- 

 rially injure the crop This was especially true of some varie- 

 ties of corn grown on the college grounds, the seed of which 

 came from the Philippine is'ands. In this case, no doubt, 

 unfavorable climatic cocditicns of that variety caused it to rust. 

 It is more severe on sweets than on the dents. At times our 

 field corn is very seriously affec'ed. 



Professor Seymour says: "The fungus is always injurious 

 to the corn on which it grows, but the extent of the injury 

 depends largely upon the age and condition of the corn and 

 c imatic conditions, and is often so slight as to be of no prac- 

 tical importance. Certa'n conditions of the weather may retard 

 the growth of the cirn and favor that of the rust. Ordinarily 

 the rust is not noticed till the latter part of the summer, when 

 the corn is well grown and not easily injured; but in the first 

 week cf July, 1886, the writer observed it repeatedly on the 

 lower leaves of partly-grown corn, whose vigor was plainly 

 impaired by it. The injury consists in loss of food materials 

 elaborated by the plant for its own growth which the mycelium 

 of the fungus uses for its growth and in destroying the power 

 of some of the tissues of the plant to do its work. 



COMMON GRASS RUST. 



This rust {Puccinia graminis^ Pers.) in several of its forms is 

 common on many grasses and especially destructive to oats and 

 wheat. The commcn rust produces three stages. One stage 

 occurs in the barberry and is known as the clust; r cup fungus. 

 This stiige makes its appearance in the northwest some time 

 during the month of June. In the latitude of Ames, a little 

 before the middle of the month. An examination of an affected 

 leaf will show small black specks on the upper surface, sur- 

 rounded by a yellow spot; this is known as the spermagonial 

 stage; the flask-shaped bodies are called spermagon'a and con- 

 tain the spermatia. These do not germinate; their function 

 is not known. A sweetish fluid, which attracts insects, is fre- 

 quently found in connection with these. Directly opposite the 

 flask-shaped bodies are small globular affairs, "cups," (Aeci- 

 dia), slightly irregular on the margins. Owing to their upward 

 growth they rupture the epidermal cells and finally the lining 



