272 



GENERAL BOTANY 



then forms spore cavities which are lined with a continuous 

 hymenial layer like that which covers the outer exposed surface 

 of a mushroom lamella. When the spores are ripe, the hymenium 

 and the hyphse of the trama, on which the hymenia of the several 

 spore cavities are borne, break down, and the spores become free 



within the peridium, or 

 outer covering. The dry- 

 ing of the entire disor- 

 ganized portion of the 

 gleba and the growth of 

 the spores result in the 

 formation of a large cen- 

 tral spore cavity filled 

 with ripe spores. Some 

 of the hyphse of the gleba 

 may also thicken to form 

 long-branched threads, the 

 capillitium threads, which 

 appear among the ripe 

 spores in some species. 

 The rupture of the outer 

 gleba by drying, by decay, 

 or by mechanical means 

 results in the wide dis- 

 semination of the spores 

 by the wind. The puff- 

 ball is not, therefore, as 

 completely adapted to 



spore dissemination as the mushroom, in which the elongated 

 stipe and the exposed lamellae facilitate spore scattering. 



FIG. 151. Parasitic fungus, Pleurotus ulma- 

 rius, growing in a wound on a maple tree 



After E. M. Freeman 



BRACKET FUNGI 



The bracket fungi (Fig. 151) are also closely related to the 

 mushrooms and puffballs on account of their method of forming 

 spores by means of basidia arranged in the form of hymenial 

 layers. These hymenial layers, in some species, cover either 



