320 



ECOLOGY. 



Mycorhiza. 



603. Many others of the higher plants have fungi associated with their 

 roots Such roots are mycorhiza. Many orchids have mycorhiza which arc 

 thiclv and fleshy, while the " coral-root " orchid has a coral-like mass of rhi- 

 zomes. The curious Indian-pipe (monotropa) has a system of slender roots 

 beside the closely branched mass of mycorhiza. Jn these cases the fungus lives 



Fig. 423. 

 Dodder. 



in the cells of the root and some of the threads of the fungus e.xtend to the 

 outside into the soil, and perhaps partly serve as abscirhent organs since the 

 root hairs are very rare or altogether absent on such roots. The Indian- 

 pipe plant possesses no chloropliyll, the fungus in its 'roots probably assimi- 

 lates carboriaceous food from decaying organic matter in the soil, and gives 

 it up to its host. 



604. Mycorhiza with the fungus in the roots are endotropic mycorhiza. 

 The root tubercles of the legumes also belong to this class. Edotropic my- 



