468 COMPARATIVE MORPHOLOGY OF FUNGI 



the basidium to secure spore dispersal has been lost and its function 

 assumed by the fructification as a whole, e.g. , by the odor attracting rodents 

 which eat the fructifications and disperse the spores in their feces, by 

 the dustiness and capillitium of the gleba which enables pressure by 

 wind or animals upon the sides of the fructification to puff out a cloud 

 of spores, whence the name puff-balls, or by the elevation of the gleba 

 upon a stipe, attracting insects which carry away the spores from the 

 autolyzing gleba. 



The peridium in the lower forms is a simple layer of plectenchyma 

 undifferentiated from the ground tissue of the developing fructification. 

 From these we may get a gradual disappearance of the peridium or its 

 differentiation into several layers with varied and important ecological 

 functions. 



The Gasteromycetes are a mixture of various genera which possibly 

 belong to entirely different development series. The following classifi- 

 cation rests upon the differences in the place of the hymenial fundament 

 and the direction of growth of the tramal plates. The first group in which 

 the hymenium is formed in thick, more or less isodiametric knots of 

 tissue (which have arisen by the pulling apart of the ground tissue) 

 almost simultaneously from the center outward, throughout the whole 

 fructification, includes the Rhizopogonaceae, Sclerodermataceae and 

 Lycoperdaceae. A second group, in which the hymenium arises within 

 a few closed chambers isolated at maturity, includes the Sphaerobolaceae 

 and Nidulariaceae. In the third group the tramal plates are regularly 

 arranged, start at definite points and grow in a definite direction. In the 

 Hymenogasteraceae they grow basipetally, in the Hysterangiaceae and 

 Clathraceae they grow centrifugally from a central part and in the 

 Phallaceae, centripetally from the periphery. 



Rhizopogonaceae. — This family includes hypogaeous or epigaeous 

 genera with a gelatinous gleba of schizogenetic cavities. The fructifica- 

 tion is surrounded by a surface layer of ground tissue (simplex peridium 

 of Zeller and C. W. Dodge, 1918), or by a more or less differentiated 

 peridium outside the ground tissue (duplex peridium of Zeller and C. W. 

 Dodge) . 



One of the more primitive forms is the cosmopolitan Rhizopogon 

 rubescens. Its fructification arises as a small knob, on a slender mycelial 

 thread, whose rind becomes the peridium and whose core, which consists 

 of hyphae of variable thickness, continues in the ground tissue of the 

 fundament (Rehsteiner, 1892). The ground tissue is differentiated by a 

 separation of the hyphae into compacter and looser tissues. The looser 

 parts which run between the thicker knots, become still looser and finally 

 form irregular cavities which are penetrated by single, thick, septate 

 hyphae. From the periphery (Fig. 297, C), new hyphal knots are con- 

 tinually differentiated along with the increasing growth of the fructifi- 



