248 



FORMS OF GASTEROMYCETES 



balls. In the earth stars (Fig. 173) the outer layer of the peri- 

 derm splits into rather regular star-like segments or valves which 

 are hygroscopic. In damp weather these valves roll back, in 



Fig. 172. Diagram of a section of one of the puffballs, showing the thick 

 skin of periderm and the irregular cavities which are lined with basidia. At 

 the base the larger, sterile cavities of the stipe are shown. 



some species to such an extent as to lift the puff ball from the 

 ground, when it may be set rolling by the wind and thus bring 

 about a better discharge of the spores. 



Fig. 173. One of the puff-balls popularly known as "earth stars," show- 

 ing the outer periderm splitting into star-like sections and the inner peri- 

 derm opening by a pore. 



98. Order e. Nidulariales or Bird's-Nest Fungi. — These mi- 

 nute and curious fungi may be found growing upon twigs or 

 upon bare ground in old fields, or upon dried dung (Fig. 174, A).m 

 They differ chiefly from the puff balls in that the spore-bearing 

 cavities are surrounded by tougher hyphae. Consequently, when 

 the periderm of these little cup-shaped bodies open, these tougher 

 parts appear as minute eggs in a nest (Fig. 174, B). 



