THE FUNGI : ASCOMYCETES AND BASIDIOMYCETES 319 



It is to this group that the 

 mushrooms and toadstools belong. 

 Many occur on the ground, some 

 are produced on dead or decaying 

 wood, whilst a few live parasiti- 

 cally on trees. Many of them form 

 what is known as a mycorrhizal 

 association with flowering plants 

 among which they live. We shall 

 consider later on (see Volume IV) 

 the details of this association. It is 

 sufficient for us to note at this stage 

 that many toadstools can live only in 

 association with particular plants, 

 especially trees, and it is for this 

 reason that we frequently find cer- 

 tain kinds of toadstools restricted 

 to certain types of woodlands. For 

 example, the common Fly Agaric 

 forms a mycorrhizal association with 

 the roots of the common Birch, and 

 it is for this reason that this par- 

 ticular toadstool is most commonly 

 found in a Birch wood. In some 

 instances this association between 

 the Fungus and the higher plant 

 leads to the formation of what are 

 called Fairy Rings. These are 

 particularly noticeable on sheep- 

 cropped grassland, where we find 

 a difi^erence in the colour of the 

 grass closely associated with a ring 

 of fruiting bodies. Not all Fairy 

 Rings show these changes in the 

 colour of the grass, since the asso- 

 ciation between the Fungus and 

 the host varies. i\t least three 

 distinct types of Fairy Rings are 

 recognized. The explanation of 

 such a ring is interesting, in bring- 

 ing out the relation between the 

 Fungus and the grass (Fig. 311). 

 On germination of the spore a 

 mycelium develops, which radiates 

 out equally in all directions. The 

 hyphae attack the roots of the grass, 



x; 



c 



<u 



V 



■S 



■M 



V 



C 

 o 



o 



C 



U ,-15 



c '^ 

 u 



£ i2 



w 







ii 



J3 



5 ao 



O ^ 

 u 



G cs 

 O 



'^ 5 



u 3 



V 



o sL 



M 





