162 IOWA ACADEMY OF SCIENCES. 



INOCULATION EXPERIMENTS WITH GYMNOSPORAN 

 GIUM MACROPUS LK. 



BY F. C. STEWART AND G. W. CARVER. 



The family of true rusts, Uredinese, is very interesting to 

 the mycologist and important to the agriculturist. It contains 

 about twenty- seven genera and a multitude of species, all of 

 which are strict parasites, living within the tissues of their 

 hosts. Several of the species produce destructive diseases in 

 cultivated plants; as examples note the rust of wheat, oats and 

 other grasses {Puccinia graminis, Pers.), blackberry rust 

 {Cceoma luminatum, Schw.), and carnation rust {Uromyces 

 caryojJhyUinus [Schrank], Schrceter). Thus far all attempts 

 to cultivate the rusts upon artificial media have failed. Conse- 

 quently the life histories of some species are imperfectly 

 known. The determination of the life histories of some species 

 is made still more difficult because of the fact that they do not 

 complete their development upon a single species of host- 

 plant, but inhabit different species at different stages in their 

 development. The life history of the common wheat rust, 

 Puccinia graminis, so frequently used to illustrate this peculi- 

 arity of rusts, is so familiar to readers of botanical literature 

 that it is unnecessary to repeat it here. It is sufficient to state 

 that wheat rust has three stages, two of which are fouad upon 

 the wheat or some other grass plant and upon the common 

 barberry (Berberis). 



The species of Gymnosporartgiutn belong to this class of 

 pleomorphic rusts. There are two forms, representing two 

 stages in the development of the fuDgus. Until about ten 

 years ago these two forms were supposed to be distinct species 

 and were given separate names. The Gymnosporangium form 

 (considered to be the higher form) inhabits, exclusively, 

 species of the Cupressineee, a group of the family of cone bear- 

 ing trees, Coniferse. The other form has received the name 



