PROTOBASIDIOMYCETES 



427 



XXIII. ORANGE RUST OF RASPBERRY AND BLACKBERRY 

 Gymnoconia Peckiana (Howe) Tranz. 



CLINTON, G. P. Orange Rust of Raspberry and Blackberry. 111. Agl. Exp. 



Sta. Built. 29: 273-296. pis. 1-4, 1893. 

 FARI.I >\v. W. G. Notes on Some Species in the Third and Eleventh Centuries 



of Ellis's North American Fungi. Proc. Amer. Acad. Arts and Sci., N. S. 



18: 65-85(76). 1883. 

 XK\V< OMIIK. F. C. Perennial Mycelium of the Fungus of Blackberry Rust. 



Journ. Mycology 6 : 106-107. pis. 5, 6. 1890. 

 RICHARDS, H. M. On the Development of the Spermogonium of Caeoma 



nitens (Schw.). Proc. Amer. Acad. Arts and Sci., N. S. 20 : 30-36. pi. /. 



1893. 

 TRAXZSCHEL, W. Culturversuche mit Casoma interstitiale Schlechtd. (= C. 



nitens Schw.). Hedwigia 32 : 257-259. 1893. 



Occurrence and symptoms. The orange rust is a common disease 

 of black raspberries and blackberries throughout portions of the 

 United States and Canada, and it is also widely distributed in 

 Europe and Asia. It is found upon various species of the genus 

 Rubus, whether wild or cultivated, although there is considerable 

 difference in the susceptibility of different varieties of the same 

 species. Among raspberries Clinton has cited the Kittatinny as 

 perhaps the worst affected, and the Snyder as notably resistant. 

 In other regions, however, the latter has proved less resistant. 

 The fungus may be noted almost as soon as the young leaves be- 

 gin to appear in the spring. The spermogonial stage appears first 

 and gives to the surface of leaves and even young stems a glandu- 

 lar appearance, which may often be mistaken for a natural condi- 

 tion. A comparison, however, of affected with unaffected plants 

 readily demonstrates the specific effects of the fungus. At times 

 the spermogonia are, however, limited in distribution, affecting only 

 a portion of the leaves of a bud, or merely small areas upon a 

 ingle leaf. In from ten to fifteen days after the appearance of 

 the spermogonia the striking aecidial stage may be found appear- 

 ing only on the lower surface of the leaf. The cushions which 

 produce the spores are rapidly developed beneath the epidermis, 

 and upon the rupture of the latter the bright orange spores are 

 disclosed. Eventually the under surfaces of the leaves may ap- 

 pear to be covered with a continuous mass of more or less adhe- 

 sive orange-red material. All of the vegetative parts of the plant 

 which are affected are usually greatly impaired in vitality and 



