STUDIES IN SYMBIOSIS. 



I. The Mycoehiza of Dipodium punctatum R. Br. 



By John McLuckie, M.A., D.Se., Lecturer in Plant Fliysiology, Univei-sity 

 of Sydney. 



Introduction. 



As investigation into the nature and physiological signifieance of mycorhiza 

 proceeds, it is becoming more and more convincing that many of the higher 

 land plants of the Bush and the Forest derive some substances from the humus 

 of the soil in a highly organised state — that the roots of a plant not only supply 

 it with water and inorganic salts, but also, with dissolved organic matter. Acton 

 (1889) has shown that carbohydrates and similar organic substances, and other 

 organic constituents of humus may be absorbed by the root of an ordinary 

 green plant. This absorption is probably independent of light and chlorophyll 

 as in the holosaprophytes, e.g., Thismia (Groom, 1895), Monotropa, etc. Sap- 

 rophytic fungi which have no relation to the roots of plants must derive their 

 carbohydrate from the humns constituents of the soil, and when they are as- 

 sociated with higher plants in the formation of exotrophic or endotrophie 

 mycorhiza, they would appear to supply some of the carbonaceous food and 

 the nitrogenous food for the higher symbiont. 



In cases of complete saprophytism amongst higher plants, the loss of 

 chlorophyll is probably the result rather than the cause of the association with 

 the mycorhizic fungus, for, when a plant obtains part of its food, especially 

 carbohydrate food, from the soil, there is not the same necessity for a very' 

 vigorous photosynthesis. In shaded situations, light may be too feeble for active 

 photosynthesis and the higher plant tends to depend more and more upon a 

 saprophytic mode of nutrition. It is probably in this way that holosaprophytism 

 has originated amongst Phanerogams. 



The green plant is essentially adapted to the synthesis of its food from 

 simple compounds with the assistance of radiant energy. Any de-sdation from 

 this normal mode of nutrition results in the modification of the chlorophyll 

 organs, the absorbing organs or both. Generally speaking the absorbing organs 

 are the first to show indications of reduction or modification as the probable 



