IRREGULAR NUTRITION 



195 



In these respects Fungi are better equipped than ordinary green 

 Plants, and it is this which makes a coahtion with tliem a pliysiological 

 advantage. Mycorhiza may 

 even lead indirectly to a state 

 of saprophytic nutrition. 



Two different types of this 

 coaJition are recognised. In 

 the first the fungus lives out- 

 side the tissues of the plant 

 with which it is related ; this is 

 described as ectotrophic, and it 

 occurs in the Beech, Horn- 

 beam, Oak, and Scots Pine ; 

 also in Monotropa, and Sarcodes 

 (Fig. 147). In the second the 

 fungus penetrates the tissues, 

 and it is accordingly styled 

 endotropJiic ; it occurs in the 

 Heaths and Orchids, and in 

 the Club-Mosses and Adder's- 

 tongues. 



[a) Ectotrophic Mycorhiz.\. 



Externally roots showing 

 ectotrophic mycorMza appear 

 wrapped round by a covering 

 of fungal origin, and are short 

 and thick, and repeatedly 

 branched. The branching is 

 sometimes endogenous as in 

 ordinary roots ; but in other 

 cases it is of external origin, 

 with transition to forking in 

 the Scots Pine. Sections show 

 that the roots are covered by 

 a thick felt ot matted fungal 

 threads, which sometimes stop 

 short of the tip [Monotropa], 

 but usuallv cover it com- 



FiG. 147 

 Whole plant of Sarcodes, sho^\ing 



ihe myrorliizic 

 root-system, from which arises a bulky flesh-coloured 

 shoot, with broad sheathing scales below, and a ter- 

 , 1 ' -n ■ ' T- /-■ ^ ■ ininal intloresrence with prominent bracts. Rodviced. 



^\tte\y [Finns, PagliS^CaypUVUS, (After Oliver.) 



