BY JOHN MCLUCKIE. 309 



pears that the host nourishes and nurtures the fungus for a time and then 

 destroys part of it as its own requirements for proteid must be met. Much the 

 same relation between host and fungus must subsist in lichens; the algae are 

 permitted to multiply, to supply the earbonaecous food of the fungus, but some 

 individuals are being constantly destroyed by the fungus. In Dipodium the host 

 is the destroyer of the fungus, and in such a case, Frank's view that endophytic 

 mycorhiza is simply fungus-trap (Pilzfalle) and that the host is a fungus- 

 digesting plant is largely correct. 



In this study of the nutritive relation between Dipodium and its endophjiiic 

 fungus, I am of the opinion that the fungus supplies the host with water, mineral 

 substances, and organic compounds from the humus; from these the host obtains 

 the ash constituents, and manufactures the starch which is seen in the cells of 

 the cortex and pith of the host. The nitrogen which occurs in humus in a poorly 

 oxygenated condition, is also absorbed by the fungus, and converted into proteid 

 which is assimilated by the host-cells during the digestion of the fungus. The 

 fungus at first obtains larger and more suitable supplies of carbonaceous food 

 from the host for growth and the synthesis of proteid. 



The mycorhiza of Dipodium, and probably of many other holosaprophytie 

 Angiosperms, is indispensable to the higher plant. 



Summary. 



Dipodium punctatum is a holosaprophytie orchid which grows in the humus 

 under Eucalypts. It is not parasitic upon roots as is stated in Moore and Betehe 

 (Flora of New South Wales). It is non-chlorophylliferous, the leaves being re- 

 duced to sro^U protective scales on the flowering axis. 



The cortex of the root contains an endophytic fungus which forms close 

 coils in the cytoplasm and in the vicinity of the nucleus. 



The fungus enters the cortex through the passage cells in the exodermis. It 

 penetrates the cortical cells and grows towards the nucleus where it branches 

 and coils. 



Starch is present in the uninfected host-cells, but disappears soon after the 

 penetration of the fungus. 



The protoplasmic contents of the hyphae stain more deeply with methyl 

 violet; they become more granular and less vacuolated. 



The nucleus of the host-cell shifts its position from time to time, but many 

 hyphae maintain close contact with it. Its membrane is frequently pushed in- 

 wards and it may assume a peculiar shape. 



The central hyphae gradually become disorganised, all structure disappear- 

 ing. The nucleus of the host-cell enlarges; its nucleolus and chromatin stain 

 more deeply. The nucleolus also increases in size. 



When the hyphae are completely digested, droplets of a yellowish waste 

 matter remain. Certain of the hyphae on the periphery of the cell and the 

 disintegTating mass grow into neighbouring cells if these are not already in- 

 fected. 



No sporangioles, bladders or vesicles develop upon the hyphae as in TMsmia. 



The fungus does not enter raphide-eells or the meristematie zone of the root. 



The penetration of the hyphae from cell to cell, and from the soil into the 

 root is probably the result of a chemotropie stimulation due to the presence of 

 a nutritive substance such as sugar in the host-cells. The growth of the hyphae 

 towards the nucleus is probably the result of the greater concentration of this 

 substance around the nucleus. 



