PLANT-LIFE IN HUMUS 



357 



These plants have become strangely modified in conse- 

 quence of their saprophytic method of obtaining food, and 

 they possess several features in common with the Toad- 

 stools : (i) their vegetative parts are embedded in the 

 humus ; (2) they obtain their food from the complex organic 

 compounds of the humus ; (3) they contain very little 

 or no chlorophyll, and so are white, yellowish, or brownish 

 in colour ; (4) only their flowering and 

 fruiting shoots come above ground. 

 Under such circumstances green leaves 

 are not needed, and they are reduced 

 to mere scales. 



The rhizome of the Bird's-nest 

 Orchid gives off into the humus a 

 tangled mass of underground stems 

 and roots which resemble a bird's 

 nest, hence its name. They are in- 

 vested with a mycorrhiza, the hyphae 

 of which are attracted to and enter 

 the absorbing cells. The Coral-root 

 (Fig. 228) does not develop roots at 

 all ; its rhizome (rh) is short and 

 much branched, and from it many 

 absorbing root-hairs are given off. 



The Yellow Bird's-nest (Monotropa 

 Hypopitys) grows in the humus of 

 shady woods, and it was on this plant 

 that mycorrhiza was first discovered. 

 From its underground stem is given 

 roots which are covered with fungal hyphae, and these 

 provide food for the Yellow Bird's-nest from the humus 

 they are decomposing. 



It is common for Fungi to live at the expense of green 

 plants, but it rarely happens that flowering plants are able 

 to live upon the labour of the fungus. 



Fig. 228. 



Coral-root Orchid. 



rh, rhizome. 



off a dense mat of 



