EXOBASIDIUM PENIOPHORA. 109 



Exobasidium rhododendri. Cramer. 



Forming gall-like, bullate excrescences, that are at first 

 pale, then reddish and shining, ^-1 in. across, on the under 

 surface of the leaves, also on the petioles and stems ; spores 

 7-8 X 3 /x, often slightly curved. 



Exobasidium rhododendri, Cramer, in Eab., Fung. Eur. r 

 n. 1910 ; Sacc., Syll. vi. n. 7797. 



On the leaves and twigs of Rhododendron ferruginvum and 

 other species. 



PENIOPHOKA. Cooke. (fig. 7, p. 94.) 



Entirely adnate or with the margin free and more or less- 

 elevated; hymenium even, furnished with projecting, fusi- 

 form, colourless cystidia, which are covered with minute 

 particles of oxalate of lime ; spores colourless. 



Peniphora, Cke., Grev., v. viii. p. 20 ; Mass., Mon. Thel. r 

 p. 140, pi. xlviii. figs. 14-19. 



The species constituting the present genus were formerly 

 included in the old genus Corticium. The leading idea of the 

 genus Peniophora consists in the presence of numerous pro- 

 jecting cells which give to the hymenium a minutely velvety 

 appearance when seen under a pocket-lens. These projecting 

 cells were called metuloids by Cooke, but they are evidently 

 homologous with the bodies called cystidia by the old myco- 

 logists. In the present genus the cystidia are unicellular, 

 colourless, more or less fusiform and with the portion pro- 

 jecting above the surface of the hymenium studded with 

 numerous minute particles of oxalate of lime. While con- 

 stituting an excellent generic character, cystidia are variable 

 in size in the same species, and even in the same specimen, 

 the measurements given refer to the length above the 

 surface of the hymenium and width at the widest part, and 

 represent the average size. In old specimens the cystidia 

 often break away, leaving the surface of the hymenium 

 glabrous, but the persistent bases can always be seen in a 

 section under the microscope. 



A. Margin free, more or less upturned. 



Peniophora quercina. Cooke. 

 Subcartilaginous, at first adpressed, the margin eventually 



