472 COMPARATIVE MORPHOLOGY OF FUNGI 



ruptures irregularly and the spores are blown away by wind or washed 

 away by rain. 



In the cosmopolitan Pisolithus (Polysaccum), the fructifications are 

 similarly formed but the maturing process takes place basipetally. 

 When the gleba is colored dark above, the lower portion is still white. 

 The trama splits, allowing the single spherical cavities to be dispersed 

 separately after the disappearance of the peridium. This mechanism we 

 shall see more highly developed in the Sphaerobolaceae and Nidulariaceae. 



While no true stipe is formed in this family, in both genera when 

 growing in sandy soil, the rooting base may be so highly developed as to 

 resemble a stipe. 



Lycoperdaceae. — In Bovista nigrescens, investigated by Rehsteiner 

 (1892), the fructifications arise either laterally or terminally on mycelial 

 threads. In contrast to other Gasteromycetes, its rind does not seem 

 to continue into the peridium of the fructification, but forms only a patelli- 

 form sheath which surrounds and protects the delicate basal part of the 

 young fungus. Furthermore, the thick, wide-lumened hyphae of the core 

 do not continue into the core of the young fructification, but the fructifica- 

 tion is built of thin-walled, narrow hyphae which run in the core of the 

 rhizmorph beside the conducting hyphae. 



These hyphae radiate more or less distinctly toward the periphery; 

 they are parallel and wide lumened, with clavate or flask-shaped tips, and 

 they form the fundament of the outer peridium. Later, as in Rhizopogon, 

 there are differentiated from the homogeneous core thicker and looser por- 

 tions of tissue; the latter develop to cavities, the former to the knots 

 with the outgrowing tramal pads. For a long time, from the original 

 ground tissue at the edge of the fructification, new hyphal knots are laid 

 down. This tissue, after fulfilling its function, grows only by the expan- 

 sion of its elements and the formation of new tramal plates. By these 

 increases in size the periphery of the ground tissue expands passively 

 and is forced apart; its tangled hyphae become solid, arranged tangenti- 

 ally and form the fundament of the inner peridium. 



As in some species of Rhizopogon, the fructifications are surrounded 

 by tramal tissue peridium but, in contrast to Rhizopogon, the outer 

 peridium is further differentiated into a radially disposed outer and a 

 tangled inner layer consisting of slender hyphae. In time, the outer 

 parts of this tangled zone swell up strongly and expand to a pseudoparen- 

 chymatous tissue. Consequently, the mature fructification is surrounded 

 by four layers : the compact trama or inner peridium, the narrow zone of 

 tangled, unthickened hyphae gradually merging with the broad pseudo- 

 parenchymatous zone which bears the outermost layer of swollen radiat- 

 ing cells. With increasing age, the outer layer becomes frayed and dried. 



In the course of the development of the gleba from the slender tramal 

 hyphae, there are differentiated solid, mostly aseptate branches which 



