MAIZE RUST. 67 



This rust is also reported from South America, Germany, France, Italy, 

 Portugal, India, and south Africa; but owing to the facts that the genus 

 Sorghum is included with its hosts and that Barclay has shown (5, Vol. 

 XXVIII, pp. 257-259; 3, pp. 21-1, 215) that the rust ou Soryhiim vulgare 

 in India is a distinct species, whicli he called P. pennisetij it is ques- 

 tionable whether it actually occurs in all these countries. 



Wintering of the iiredo. — This rust is not yet known to winter its 

 uredo in any country, and as no iccidial stage has been discovered, the 

 manner of its i^erpetuation throughout the year is entirely unknown. 



Liahility of iJ iff event varieties to this rust. — There is as yet no differ- 

 ence known in the susceptibility of different varieties of corn to this 

 rust, but so far no investigations have been made to determine this 

 point. The rust seems to be of but little economic import-ance. 



Damage. — The writer has occasionally seen patches of very late corn 

 injured by this rust. If corn is sown broadcast as a forage crop late in 

 the season it is likely to bo badly damaged, but as a rule the rust does 

 little or no damage. Pammel mentions (oOa, p. 854) that in Iowa the 

 yield of corn, especially of sweet corn, is sometimes materially lessened 

 because of rust. 



(iENEKAL REMARKS. 



Many inoculation, germination, and other physiological exi)eriments 

 not mentioned in this bulletin but bearing closely on the cereal rust 

 IDroblem, Avill be discussed in other publications of this Division. These 

 experiments, like those made by Eriksson, show that in addition to 

 the forms herein described, the cereal rusts have also distinct si)ecial- 

 ized forms on various grasses, but as these forms do not occur on the 

 cereals they are usually of no econonaic importance. In addition to the 

 experiments already reported in a former publication (15, pp. 448-452), 

 numerous others were made b}^ the writer to determine the behav- 

 ior of the uredospores from a chemical standpoint. Also hundreds of 

 inoculations on cereals with the iiicidia of various plants other than 

 barberry have been made for the purpose of discovering, if possible, 

 other a'cidial hosts for the cereal rusts, but so far none have been 

 found. Again, the morphological differences between the different 

 forms of the cereal rusts are, in a few cases at least, of considerable 

 imiwrtance, but it is thought best, under the circumstances, to discuss 

 them in another publication. 



Something should be said concerning the value of the inoculation 

 experiments reported in this bulletin. It may be claimed by some that 

 the experiments which proved successful in the greenhouse and on 

 young plants would probably result negatively in a greater number of 

 cases if made out of doors on more mature plants. This is not only 

 possible, but, as already shown, the writer's results make it very i)rob- 

 able; and thereby the experiments are all the more valuable, as in the 

 greenhouse they are more exclusive in nature and in no case is an 

 infection likely to take place out of doors if it can not be x)roduced in 



