GRASSES OF IOWA. 265 



short account by one of us,* and one by Weed+ in his book, 

 "Fungi and Fungicides. " 



Characters of the fungus. — The fungus produces two stages. 

 The first cr uredo stage is similar to the red rust stage of 

 wheat. It occurs on the bracts covering the cob, leaves and 

 sheath. SmaU, light-brown pustules or sori appear on both 

 surfaces of the lea**. Close examination will show that these 

 sori break through the epidermis where small white spots 

 occur. The rupturing of the epidermis is caused by the con- 

 tinued growth of the spores underneath. The ruptured epi- 

 dermis shows the small spores. The uredo spores are one- 

 celled, round or more often elongated and spiny. The stalk is 

 detached. The spores measure 23-38 x 20-26". The uredo sori 

 are clustered or arranged in parallel rows, closely following 

 the veins of the leaf. The uredo spores are capable of germi- 

 nating immediately ani distribute the fungus during the sum- 

 mer. They preserve their vitality for oaly a short time; at 

 any rate they do not live through the winter. Carletont states 

 that the time of incubation for the uredo is shorter than any 

 of our cereals, varying from five to eight days. 



As the leaves become older the yellowish-brawn uredo sori 

 are replaced by black sori. These sori may also appear where 

 uredo sori did not occur. The same mycelium which gave rise 

 to the uredo spores later gives rise to the teleuto spores. The 

 sori containing these spores are black. The spore is broadly 

 elliptical and two-celled. It measures 30-52 x 16-24". The 

 apex may be thickened and somewhat pointed. These spores 

 preserve their vitality for some time; they are dormant through 

 the winter. In the spring each cell may germinate by produc- 

 icg a tube, known as the promycelium, which bears laternal 

 bodies known as sporidia. It is undoubtedly connected with 

 some aecidium or cluster cup stage, but this stage is not known. 

 Carletoa reports the occurrence of this fungus on Teosinte 

 {Euchlaena mexicana) which is closely related to maize. 



The species is of considerable economic importanc3 in our 

 state, but it is seldom that reference is made to it. Duthie and 

 Fuller§ state that corn is singularly free in India from fungus 

 diseases. Agricultural writers in this country do not usually 



♦Pammel. Monthly Review of the Iowa Weather and Orop Service. 7: 7.1898. 



+Weed. Fungi and Fungicides. 207, 8, 80. 



$Oereal Rusts of the United States. 66. 



gField and Garden Crops of Northwestern Province. Ouah. etc. 1: 21. 



