SUBCLASS EUBASIDIAE 465 



them have arisen from one or more of the gasteromycetal orders. In the 

 arrangement here set forth the majority are beheved to form one series 

 with a few forms of more doubtful origin. 



Apparently the most primitive forms produced resupinate spore fruits 

 with the basidia scattered or packed close together, and without a very 

 definite hmit of growth to the hymenium. By the formation of folds, 

 ridges, teeth, etc., the hymenial surface became increased in the various 

 families. At the same time a tendency appeared toward confining the 

 hymenium to the under side of laterally attached or centrally stalked 

 spore fruits. These spore fruits vary from felty to fleshy or leathery or 

 corky or woody in consistence and may function for only a few hours or 

 days, in some of the fleshy sorts, to many years in some of the corky or 

 woody species. The size may vary from a few millimeters to over a meter 

 in diameter and from a few layers of cells in thickness to 30 or 40 cm. 

 A few species are obligate parasites in the stems, leaves, fruits, and 

 flowers of Anthophyta (Angiosperms), e.g., Exobasidium. Some are para- 

 sitic or saprophytic depending upon the environment or opportunity, 

 e.g., Pellicularia filamentosa (Pat.) Rogers {Corticium vagum var. solani 

 Burt ex Rolfs). Many are parasitic upon the roots of plants, killing them 

 and some extend up into the stem, kiUing the bark. Some are saprophytic 

 on humus, decaying leaves, stems, etc. The nonliving woodcells of living 

 trees may be attacked and the wood rotted without actually any parasitic 

 action upon the living cells of the trunk. The weakening of the stem by the 

 decaying of its woody elements may cause it to break, thus leading to its 

 death. Schizophyllum commune Fr. may attack some trees as parasites 

 but may be saprophytic on others. Many of the more woody or corky or 

 leathery species are capable of culture in the laboratory but many of the 

 fleshy forms have resisted all such attempts as yet. 



The hymenium may consist entirely of basidia all of the same age or 

 with younger basidia pushing up between the older ones. The newer 

 basidia may push out beyond those first formed so as to increase the 

 thickness of the hymenium which may then show definite or indefinite 

 layers. In a great number of forms where the development of the spore 

 fruit is not limited by the formation of a definite border of different struc- 

 ture the centrally produced basidia are the oldest and around them 

 additional basidia arise successively further and further from the center. 

 As a result in such species all ages of basidia may be found on making a 

 radial section, from the oldest ones near the center to those near the 

 margin which are just beginning to develop. 



The basidia vary greatly in shape in the Hymenomycetes. They are 

 usuaUy round in cross section but when crowded laterally may become 

 somewhat angular. They may be cylindrical, tapering at the very base 

 and rounded at the apex, or urn-shaped or clavate or almost globose. 



