13 



CLASS BASIDIOMYCETEAE: 

 SUBCLASS HETEROBASIDIAE 



IN THE basidial structure of one of its orders, the Auriculariales, this 

 subclass shows many points of similarity with the more typical forms 

 of Subclass Teliosporeae. By some authors (e.g., Patouillard, 1900) the 

 latter are included in this order. Taking all their characteristics into con- 

 sideration it seems to the author to be a more satisfactory arrangement to 

 keep them apart in separate, but more or less closely related, subclasses. 

 Thus limited the Heterobasidiae consist of fungi most often living as 

 saprophytes upon wood or other plant materials but in some cases para- 

 sitic upon living plant tissues or even upon insects (e.g., Septobasidium) . 

 They form their spore fruits as thin or thick layers or projecting cushions 

 or clubs or shelves of basidium-forming tissue. The basidia are formed 

 mostly in a more or less recognizable layer, the hymenium, often crowded 

 side by side in a palisade-like arrangement, and shoot their basidiospores 

 off into the air with the exception of one or two genera. The basidiospores 

 frequently become septate as they mature or after they are discharged 

 and as a general rule (to which there are exceptions), germinate by the 

 formation of numerous small buds when they fall into water, though 

 capable of producing germ tubes under favorable conditions. In many 

 cases a basidiospore will form a small sterigma and a secondary spore will 

 be shot off, just as occurs frequently in the formation of secondary spo- 

 ridia in the Uredinales. The spore fruits are more often waxy, or gelatinous 

 when wet, and frequently dry down to rather inconspicuous horny masses 

 when dry. This is made possible by the fact that the outer portion of the 

 wall of each hypha swells greatly upon absorbing water. 



The basidial characters that further distinguish this subclass from 

 Subclass Eubasidiae are the following: In the Eubasidiae the basidium 

 remains as one cell usually bearing the Ijasidiospores at its upper end on 

 short or long sterigmata. Tulostoma and one or two related genera form 

 an exception in that the sterigmata may be formed laterally on the 



436 



