POLYPORALES 



435 



fleshy cushions, as Platygloea in the Auriculariales and Sebacina in the 

 Tremellales, and may be designated as true crustose fructifications. Their 

 basidia rise to the same height, and crowd together as an even hymenium 

 which is broken only by cystidia. In the third stage, the hyphal cushions 

 increase to bracket or even centrally stipitate fructifications. The context 

 loses its homogeneous structure and is differentiated into a sclerotic rind 

 and solid middle layer. Thereby, they become very resistant to external 

 influences ; while the hyphal tissue of the first two groups appears in damp 

 weather and in drought collapses and becomes invisible, or is entirely 

 ephemeral, the fructifications of this third group survive climatic varia- 

 tions and at times attain great age. 



1 





-- **o^ 





,s S_S 





Fig. 277. — Hirsutella varians. 1. Habit. 2. Conidia. 3. Apparently a transitional 

 stage from conidia to one- and two-spored basidia. 4. Basidia. (1 X16;2, 3 X390;4 X 

 780; after Boulanger, 1893.) 



In the first group are many species of Exobasidium (see p. 413), 

 Hypochnus, Hirsutella and a small group of semiparasitic species of 

 Corticium, while the remainder of Corticium belongs rather to the second 

 group. In Hypochnus and Corticium, the basidia are borne on a resupi- 

 nate hyphal tissue, in Hirsutella, on coremia. All three groups form very 

 loose, flocculent or mealy, white or bright-colored wefts which in the 

 higher species thicken to a fibrous tissue. At maturity, the hyphae 

 branch and form basidia on their ends. In many species, the sub- 

 terminal cell grows laterally to a new basidium which pushes the old one 

 aside and later is itself pushed aside by the younger ones. By the 

 continuous formation of new basidia and groups of basidia, the basidial 

 layer becomes thicker and thicker and in some species gradually develops 

 to a more or less continuous hymenium. 



