THALLOPHYTES: FUNGI 



285 



is reported. The life history seems simple, but this appar- 

 ent simplicity may represent a very complicated history. 

 The structure of the common mushroom (Agaricus) will 

 serve as an illustration of the group (Fig. 255). 



190. A common 

 mushroom. — The 

 mycelium, of white 

 branching threads, 

 spreads extensively 

 through the decay- 

 ing substratum, 

 and in cultivated 

 forms is spoken of 

 as the " spawn." 

 Upon this myce- 

 lium little knob- 

 like protuberances 

 begin to arise, gro w- 

 ing larger and 

 larger, until they 

 are organized into 

 the so-called 

 "mushrooms." 

 The real body of 

 the plant is the 

 white thread - like 

 mycelium, while 

 the " mushroom " 

 part seems to rep- 

 resent a great num- 

 ber of sporophores 

 organized together 

 to form a single 

 complex spore- 

 bearing structure. 



The mushroom 



Fig. 256. A common Agaricus : A, section through one 

 side of pilens, showing sections of the pendent gills; 

 B, section of a gill more enlarged, showing the cen- 

 tral tissue, and the broad border formed by the ba- 

 sidia : C, still more enlarged section of one side of 

 a gill, showing the club-shaped basidia standing at 

 right angles to the surface, and sending out a pair 

 of small branches, each of which bears a single ba- 

 sidiospore.— After Sachs. 



