246 



PKACTICAL BOTANY 



distributed over asparagus beds. 1 The hollyhock and many 

 other members of the mallow family (Malvacecz), to which the 

 hollyhock belongs, are often all but destroyed by the holly- 

 hock rust (Pucdnia Malvacearum). jEcidial stages of other 

 rusts appear upon many common plants, as the May apple, 

 jack-in-the-pulpit, burdock, sunflower, and blackberry. 



Apple rust and 

 " cedar apples," 

 produced by the 

 rust G-ymnospo- 

 rangium macro- 

 pus^ offer a strik- 

 ing life cycle. 

 Upon red cedar 

 trees in the late 

 autumn, winter, 

 and early spring 

 branches may be 

 found with hard 

 brownish knots 

 upon them (Fig. 

 200). The knots 

 are outgrowths 

 produced by the 

 internal myceli- 

 um of the rust. 

 Near or before the period in the spring when apple trees are in 

 flower or setting young fruit, the brownish knots or " cedar 

 apples" become gelatinous, and from them yellow projec- 

 tions protrude (Fig. 201). These projections are made up 

 of hyphse bearing teleutospores. The teleutospores germinate 

 at once, producing from one to three hyphse from each cell. 

 Sporidia are formed, and since these are blown about in great 

 profusion, some of them alight upon young leaves, flowers, or 



1 "The Asparagus Rust : its Treatment and Natural Enemies," Bulletin 

 129, N. 3. Agr. Exp. Sta., 1898. 



FIG. 200. A "cedar-apple" parasite (Gymnosporan- 



gium) as it appears in winter condition upon its host, 



the red cedar (Juniperus Virginiana) 



Natural size 



