IRREGULAR NUTRITION 197 



side of the fungus, which is already leading a saprophytic existence 

 in the soil, a direct supply of carbohydrate will be obtained by contact 

 with the root. The initial advantage from the coalition would then 

 lie with the fungus. The advantage which the trees derive is in the 

 first place the more ready supply of salts, and of combined nitrogen 

 extracted by the fungus from the soil. The hyphae establish a more 

 intimate relation with the soil than ordinary root-hairs, and there is 

 abundant evidence of their special aptitude for absorption not only 

 of such salts, but also of organic materials. These also they may 

 hand on to the root. That the relation is mutually satisfactory is 

 shown to be probable by its prevalence, and by the vitality which 

 both the parties show. 



But the importance of this form of irregular nutrition varies greatly 

 for different plants. It culminates in those cases, such as Monotropa 

 and Sar codes, in which the plant is almost, or entirely without chloro- 

 phyll of its own. Clearly the supply of all organic material, as well 

 as of water and necessary salts, is here obtained through the fungus 

 from the humus substratum. It may not perhaps be strictly true to 

 call these plants themselves saprophytes ; but the legal maxim runs, 

 " quifacit per aliumfacit per se" They are physiological " resellers " ; 

 that is, saprophytes at second-hand, being actually parasitic on a 

 saprophytic fungus. It is quite possible that in less degree the same 

 may be the case even for the Beech, Oak, and Scots Pine. 



ENDOTROPHIC MYCORHIZA. 



The essential feature of endolrophic mycorhiza is that, fungal filaments 

 occupy the living cells of the host, coming into intimate relation with their 

 protoplasts. It is stated that occasionally the ectotrophic fungus of 

 Monotropa or Sarcodes may penetrate the superficial cells, a fact 

 which suggests how the more prevalent endotrophic type may have 

 arisen. It is characteristic of Orchids, and Heaths, and is found in 

 many isolated genera, such as Paris, Anemone, and Allium, and among 

 such lower plants as Psilotum, Lycopodium, and the Ophioglossaceae. 

 A similar condition is also seen in some Bryophytes. There is great 

 variety in the colouring of these plants. Most of them show a full 

 green, and would pass perfectly as autophytes ; as for instance 

 Rhododendron, the Heaths, or Paris. Some are more or less pale in 

 colour, as in such Orchids as Goodyera, or Listera cordata. Others 

 may be without chlorophyll, showing a brownish tinge, as in the Bird's 

 Nest Orchis (Neottia), or the Coral-Root (Corallorhiza). These 



