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A TEXT-BOOK OF BOTANY 



in other cases the spores are scattered by the wind and the 

 infection starts in the tree tops. Almost all full-grown trees 

 are diseased at some point. 



86. Puffballs. The puffballs are fleshy Fungi that differ 

 from the mushrooms in having the spores enclosed until 



they are ripe (Fig. 152). 

 There is a subterranean 

 mycelium, as in the mush- 

 rooms; but the spore- 

 bearing structure is a 

 fleshy, globular body, con- 

 taining irregular cham- 

 bers lined with the spore- 

 producing layer. When 

 young, this body is solid 

 and white; but as the 

 spores mature, it becomes 

 yellowish and brownish, 

 gradually dries up, and 

 finally is only a brown 

 parchment-like shell con- 

 taining innumerable, ex- 

 ceedingly small spores 

 that are discharged by 



the breaking of the shell. Some of the puffballs become 

 very large, reaching a diameter of twelve to eighteen 

 inches. 



87. The highest group of Fungi. The rusts, mushrooms, 

 and puffballs represent the highest and most extensive 

 group of Fungi, characterized by producing spores by means 

 of a basidium, and hence called Basidiomycetes, which means 

 "basidium Fungi." The peculiarity of the basidium is 

 that it sends out branches, each of which produces a spore 

 at its tip (Fig. 147, C). The layers of basidia (spore-pro- 

 ducing cells) were noted in the mushrooms and the puff- 



FIG. 152. Puffballs. After GIBSON. 



