DEVELOPMENT OF PLANTS 



267 



dusty mass of spores and in some cases firmer hyphae, the capil- 

 litium. The skin ruptures in various ways, often- by one or 

 more pores at the top, and the least touch now causes the spores 

 to sift out* in smoke-Hke puffs, hence the popular name of puff- 

 balls. In the earth stars (Fig. 176) the outer layer of the peri- 



FiG. 176. One of the puffballs popularly known as "earth stars," show- 

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

 derm opening by a pore. 



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

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

 some species to such an extent as to lift the puffball from the 

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

 about a better discharge of the spores. 



Fig. 177. A common bird's-nest-fungus, Crucihulum: A, habit of fungus 

 on branch of hickory. B, one of the cups in section, showing the tough hyphae 

 surrounding the spore-bearing cavities. 



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

 minute and curious fungi may be found growing upon twigs or 

 upon bare ground in old fields, or upon dried dung (Fig. 177, A). 



