548 



COMPARATIVE MORPHOLOGY OF FUNGI 



basidia are formed in the uppermost portion of the crust from pyriform 

 to spherical probasidia, which are either terminal on the ends of hyphae 

 or irregularly borne on lateral branches of more or less coiled hyphae. 

 In S. frustulosum, the probasidium becomes septate and functions as a 

 basidium, as do the teliospores of the Coleosporiaceae in the next order 

 (Burt, 1916). In S. pinicola on Pinus Strobus and P. monticola, the 

 probasidia are apparently at the same stage of development as in Iola, 

 since the walls are not thickened and the basidium develops within a 

 short time (Snell, 1922). In S. retiforme and S. frustulosum, the probasi- 

 dia are colored brown, but no statement is made as to the thickness of the 

 wall. 



Fig. 366. — Septobasidium albidum. Group of conidia resembling Torula. (X400; 

 after Patouillard, 1913.) Septobasidium pseudopedicellatum. 2. Section of upper portion of 

 crust (X360). 3, 4. Germinating basidiospores. (X720; after Coker, 1920.) Septo- 

 basidium pedicellatum. 5. Development and germination of probasidia. (X260; after 

 Patouillard, 1892.) 



The more highly differentiated group of species produce a layer of 

 tissue next the substrate, from which rise hyphal pillars which support 

 the outer layer bearing the hymenium (Fig. 365). S. cirratum forms a 

 transition from the primitive group, since the pillars are of variable diam- 

 eter and composed of loosely intertwined hyphae. In many species of 

 this group the wall of the probasidium is thickened, and in S. castaneum 

 also slightly colored, hence the zeugites might be called sclerobasidia 

 (Fig. 366, 2 and 5). 



The basidiospores germinate directly to secondary spores, rarely 

 to mycelia. In S. pseudopedicellatum and S. retiforme, they divide into as 

 many as eight daughter cells before germination (Fig. 366, 3 and 4). These 

 cells produce elongate sprout cells (Coker, 1920 ; C. W. Dodge, unpublished 

 observations). In S. retiforme the basidium falls from the probasidium 



