78 



BOTANY. 



the leaves of the barberry, where it produces spores quite dif- 

 ferent from those upon the wheat ; the cedar rust, in the same 

 way, is found at one time attacking the leaves of the wild crab- 

 apple and thorn. 



FIG. 47. A, a branch of red cedar attacked by a rust (Gymnosporangium), 

 causing a so-called "cedar apple," x . B, spores of 'the same, one be- 

 ginning to germinate, x 300. C, a spore that has germinated, each cell 

 producing a short, divided filament (basidium), which in turn gives rise to 

 secondary spores (sp.), x 300. J), part of the leaf of a hawthorn attacked by the 

 cluster cup stage of the same fungus, upper side showing spermogonia, natural 

 size. E, cluster cups (Roestelia) of the same fungus, natural size. F, tip of 

 a leaf of the Indian turnip (A rixsema), bearing the cluster cup (jfScidivm) 

 stage of a rust, x 2. G, vertical section through a young cluster cup. H, 

 similar section through a mature one, x 50. /, germinating spores of //, 

 x 300. J, part of a corn leaf, with black rust, natural size. K, red rust spore 

 of the wheat rust (Puccinia yraminis), x 300. L, forms of black-rust spores : 

 I, Uromyces ; n, Puccinia ; in, Phraymidiwm. 



The first form met with in most rusts is sometimes called 

 the "cluster-cup" stage, and in many species is the only 

 stage known. In Figure 47, F, is shown a bit of the leaf of 

 the Indian turnip (Ariscemd) affected by one of these "cluster- 

 cup " forms. To the naked eye, or when slightly magnified, 



