THE FUNGUS BODY. 39 



of the more massive parts, where they are necessary to impart 

 firmness, rigidity, or durability. 



The interweaving and fusion of the hyphae sometimes pro- 

 dace cord-like or strap-like structures of considerable size. 

 The mycelia of the higher fungi frequently form them, and 

 they may be found in the leaf-mold of forests or in rotten 

 stumps or between boards in wet places. 



48. Lichens. — The body of lichens is a mycelium woven 

 about the simpler algae, rarely about other small green plants, 

 which are thus imprisoned. The fungus hyphae usually pre- 

 dominate and in great measure determine the form of the body 

 and its texture. Sometimes the algae are present in such 

 numbers that the hyphse seem merely distributed among them. 

 In form the body may be broad and thin (fig. 215), or slender 

 and shrub-like ; in some cases it is so thin and adherent, or so 

 interwoven with the substratum, that it seems to form a mere 

 crust over it. In texture it may be tough and leathery, with 

 the hyphae near the surface fused into a false tissue (a, b, fig. 

 36). When gelatinous algae, such as Nostoc (see ^11) are 

 imprisoned, the body may be gelatinous while wet. In all 

 cases the algse supply the fungus with food, and are in turn 

 supplied with water absorbed by the spongy mycelium. (See 

 further tl 164, 185, 367.) 



EXERCISE X. 



Lichen (Physcia stellaris). — Soften a plant by soaking it in water for 

 a few minutes. Observe 



1. The mycelium, forming a connected leaf-like lobed thallus. Com- 

 pare as many other forms as are available. (^ 48, fig. 215.) 



2. Compare the color when dry and wet. In the latter condition, the 

 mycelium is more translucent and the imprisoned green algse show 

 through more plainly. (Figs. 36, 216.) 



3. The tufts of hyphse extending from lower surface to bark, the hold- 

 fasts or rhizines, 



4. Occupying the central region on the upper surface, the round 

 colored disks, the clusters of spore cases. 



