442 



BOTANY OF THE LIVING PLANT 



of these Fungi. Thus in the Gasteromycetes the fructification is closed, 

 the basidia being produced internally, and the spores set free by rup- 

 ture, as in the Puff-Bails. In the 

 Hymenomycetes the basidia are borne 

 collectively in a definite layer called 

 a hymenium, exposed to the air, from 

 which the spores are shed, as in the 

 Mushrooms, Toadstools, and Shelf- 

 Fungi (Figs. 340, 341). 



The mycelium may obtain nourish- 

 ment in various ways. It is some- 

 times parasitic as in the Honey Agaric 

 (Armillaria mellea), which penetrates 

 the trunks of forest trees, ravaging the 

 cambium, and killing them (see Fig. 



292). Many OI the bhelf-rungl [Foly- Q f the radiating, downward-directed gills 



x ,, ,1 To the right a young fructification or 



pOrUS) grOW paraSltlCally at the ex- -button" Mushroom. (Reduced.) (From 



pense of the heart-wood of trees, Strasbur § er ) 



making them hollow. The infection comes through injury by wind, 

 which exposes the internal tissues to the invading spores. The 

 mycelium may live for years, digesting the lignined walls, till it is 



Fig. 341. 



Psalliota (Agaricus) campestris. Mush- 

 room. The hymenium covers the surface 



Fig. 342. 



Radial longitudinal section through wood infested with Forties igniarius. 



Highly magnified. (After Hartig.) 



sufficiently nourished to form a fruit-body (Fig. 342). On the other 

 hand the Dry Rot Fungus (Merulius lacrymans) lives saprophytically, 

 its mycelium digesting the substance from dead wood-work in houses 



