CHARACTERS OF MUSHROOMS. 



299 



flesh is very obvious when a thin section of the cap is examined 

 under the microscope, but in certain genera, as Russula and Lactarius, 

 many branches of the hyphce become greatly enlarged, forming little 

 vesicles or bladders. These vesicles lie in groups all through the 

 flesh of the pileus, sometimes forming the greater part of its sub- 

 stance. The filamentous hyphce pass around and through these 

 groups, filling up the interstices. In cross section this tissue resem- 

 bles parenchyma, and appears as if it were made up of rounded cells. 

 Such a trama is said to be vesiculose to distinguish it from the ordinary 

 or floccose trama. The threads on the outer surface of the pileus 



Figure 239. 



Portion of vesiculose trama in the pileus of a 



Russula. 



Figure 240. 

 Portion of a floccose trama. 



constitute the cortex or cuticle. They are thick walled and often 

 contain coloring matter which gives the plants their characteristic 

 color. In many species their walls become gelatinized, covering the 

 outside of the pileus with a viscid, slimy, or glutinous layer, often 

 called pellicle. In other instances the corticle layer ceases to grow 

 with the pileus. It is then torn and split by the continued expand- 

 ing of the rest of the plant, and remains on the surface in the form 

 of hairs, fibers, scales, etc. 



As an example of the most usual form of the pileus, we may take 

 that of the common mushroom {Agaricus campestris) when it is nearly 

 expanded. The pileus is then quite regular in outline and evenly 

 convex (Fig. 243). Many mushrooms during the early stages of their 

 development have this form, which is variously changed by later 



