316 



THE BASIDIOMYCETES 



Chryso77iyxa abietis on Picea sp., and Piicciiiia vivipari on Polygo- 

 niim vivipannn, pvcnia are unknown. In Cronarthnn ribicola the 

 pycnia are usually produced a year before the formation of the 



aecial stage. 



Fig. 120. Acerv^ular and pycnidial types of pycnia. A. Pycnium of Gyut- 

 nosporanghnn clavariaeforme, in section, beneath epidermis on leaf of 

 Crataegus. B. Subcuticular pvcnium of Phragviidiwn violaceinn on leaf 

 of Rubus. C. Portion of vertical section of pvcnium of Cronarthnu ribicola 

 on white-pine twig. D. Subepidermal pycnium of Milesia marginalis on 

 needle of Abies balsaviea. {A and B adapted from Blackman, C from 



Collev, and D from Hunter.) 



The position, size, color, and form of pvcnia are worth noting. 

 In most species they appear on the surface opposite that on which 

 the other stage or stages occur. Occasionally, as in Gyjnnocoma 

 inter stitialis, they are produced on both leaf surfaces. 



Pycnia vary in form from hemispherical or acervular to globu- 

 lar or pycnidial. Subcuticular or subepidermal forms are usually 

 acervular, whereas pycnidial forms are more deeply seated. Rusts 



