24 Transactions British MycologicaJ Society. 



the cells, they use up the cell-sap that passes between 

 adjoining cells. McDougall^ holds that these fungi^ are in 

 the main parasitic. This view was also held by Nadson* 

 though he agreed with Frank that while dislodging the root 

 hairs the fungus by its travelling hyph,£e had taken over the 

 provision of water and food materials, and this is 

 undoubtedly the case. 



Endotrophic mycorrhizas penetrate more deeply into the 

 tissues : they are intra- as well as inter-cellular. A very 

 exhaustive account of this type of fungus as affecting 

 Neottia Nidus-avis' was published by W. Magnus. f In 

 that orchid the fungus gains entrance into the roots, and 

 branches out occupying concentric layers of cells, three to 

 four cell rows (from without inwards), while some six rows 

 in the rhizome and stalk may be infected. The 

 fungus penetrates the cells by means of haustoria 

 which branch out within the cells forming a coil round the 

 outer wall, from which new hyphal haustoria pierce to the 

 cytoplasm of the cell and secure nourishment. Such cells 

 Magnus designates as host cells in which the fungus never 

 degenerates ; they occupy in Kcotiia the central cells of the 

 invaded tissue. In the cells of the outer and inner layers, 

 on the contrary, the fungus dies off and is digested by the 

 host protoplasm which increases rapidly ; these are termed 

 by Magnus digesting cells. Any undigested remains of 

 the hyph^ in these cells are balled together as excreted 

 material and are invested by layers of cellulose. In Neottia 

 there is no possibility of the fungus conveying food from 

 the open as it is entirely endophytic, and as Neottia possesses 

 no chlorophyll, it has been suggested that the outer root cells 

 possess a power, due to the irritant action of the fungus, 

 of absorbing carbohydrates from the humus of the soil. 



Fungi-are constantly associated with Orchids as endophytes, 

 though the arrangement of host, and digesting-cells is not 

 so regular as in Neottia. In some species the seeds will not 

 germinate without the aid of the fungus in the culture : 

 possibly some irritant is supplied. 



A very remarkable case is described by Kusano:|: in 

 Gastrodia elata, a Japanese Orchid. It forms tubers which 

 require to be infected by the rhizomorphs of Armillaria 

 mellea, before the plant can develop flower and fruit. As 

 in other Orchids, there is some resistance to the entrance 

 of the fungus in the outer zone. In a deeper layer the fungus 



§ McDdUi^all, '14. * Nadson, 'oS. t Magnus, '00. 



+ Kusano, '11. 



