IRREGULAR NUTRITION 



2<)| 



arising from cither stem or root. Throucrli these the hyphal filaments 

 pass, either outwards to estabhsh connection with the humous soil, or 

 inwards to cause new infections. (Fig. 151, p.) 



Within the Orchid family there is some variety in the application of this 

 indirect nutrition. In some cases {Bletiella), germinatKjn is independent 

 of the infection of the seedling, wliich need not occur till several le;ives have 

 been formed In the Ophrydeae, which include most of the native ground 

 Orchids with tuberous stocks, the infection is very early. It causes 

 that tuberous swelling of the sympodial stock and roots, which is repeatc<l 

 in each annual growth of these plants (Fig. 152). Most of the Orchids 

 that are thus mycorhizic possess chlorophyll, giving them a more or less full 

 green colour. They are thus only partially dependent upon the symbiosis. 



Fig. 152. 

 Genniuatioa of the Ophrydeae. .4 =^ young tuber of OrcAis in >cttion. U- young 

 plant. C = young plant of Ophrys in section. D = diagrani of young plant of 

 Platanthera, second year; /)=tuber of first year; /,< = succeeding tubers; ^-^ scales; 

 reinfected region ; f=root. (After Bernard.) 



But Others are wholly dependent, growing as complete saprophytes. The 

 most important native examples are Corallorhiza and Keottta. The former 

 grows in Pine woods with its rhizome embedded in rich humous soil. It 

 consists of freely branched underground shoots, bearing scale-leaves, but no 

 roots. The aerial part of the plant is a simple scape, bearing only colourless 

 scales, and at the top a raceme of small pale flowers. The fungus gams 

 access to the tissues through the numerous tufts of hairs scattered over tlu- 

 surface of the shoot. Digestion of the hyphae has been obscrvt-d, and .i<, 

 they disappear starch-grains are formed in the inner tissues. 



The relation of host and fungus has been worked out very fully in the 

 Bird's Nest Orchis {Neottia), which grows commonly in woods, putting up its 

 brown flowering scape in early summer. If it be dug up, the brown " bird's 

 nest " is found to consist of thick fleshy roots crowded ui)on a short ccntr.il 

 axis which bears scale leaves, with lateral buds in their axils. It is, in fact, 

 a rhizome, as in Corallorhiza ; but whereas roots arc absent here, in Seothm 

 they form the most prominent feature (Fig. 133 C, D). 



