BY JOHN MCLUCKIE. 307 



higher plant and the fungus, but in regard to endophytic mycorhiza especially, 

 it would appear that in certain eases the cytoplasmic contents of the host-ceUs 

 are destroyed, while in others the fungus suffers destruction. In Dipodium I 

 have shown that the fungiis absorbs nutritive substances from the cortical cells 

 of the host which it invades, and the protoplasm or proteid of the fungal hyphae 

 increases at the expense of starch which disappears from the infected host- 

 cells. The adjacent uninfected cells of the host contain starch even after its 

 disappearance from the infected cells. The starch reappears in smaller quantity 

 after the destruction of the hyphae. As the starch disappears the proteid and 

 protoplasmic contents of the hyphae increase, hence the carbohydrate of the 

 host-cell would appear to be used in the synthesis of nitrogenous food in the 

 mycelium. 



The nitrogen for this process is probably derived from the soil by the 

 hyphae which occur on the surface of the roots, and which are connected with 

 the hyphae in the cells of the cortex of the host. Thus far there has been a 

 gain in nitrogenous food by the fungus at the expense of the carbohydrate of 

 the host-cells. After a time the hyphae disorganise, their contents are digested, 

 the walls are dissolved, the nucleus of the host-cell enlarges, the chromatin stains 

 more deeply, the nucleolus grows, starch reappeaj-s in the cell (in smaller quan- 

 tities however) ; there is finally an excretion of yellowish highly-refractive drops 

 of waste matter in the cell. From these series of changes the inference is that 

 the nutritive exchange on this occasion is from the fungus to the host-cell; the 

 fungus is destroyed, probably by the agency of enzymes secreted by the host- 

 cytoplasm. The host-cell gains in nitrogenous food — in proteid which has been 

 synthesised by the cytoplasm of the fungus. 



It seems that in Dipodium the preponderance of the physiological advantage 

 of the mycorhizic association rests with the higher plant. Much of the fungus 

 becomes digested in the host-cells, but the cortex always contains cells with the 

 fungus in all stages of development. The mycelium is never extinguished, and 

 it is always connected to the superficial mycelia through the passage-cells. 



In Dipodium it seems that the fungal hyphae forming the mycorhiza are 

 indispensable to the host for, while the surface of the root may be capable of 

 absorbing soil constituents, e.g., water, salts, organic substances, yet the absence 

 of root-hairs, and the consequent small absorbing surface points to its ineffective- 

 ness as an absorbing organ. The host-plant, being devoid of chlorophyll, is 

 incapable of photosynthesis; being devoid of root-hairs it is dependent upon the 

 fungus for its supplies of H2O, C, N, etc. 



The humus of the soil in which Dipodium grows contains carbonaceous and 

 nitrogenous matter, and the host-plant derives these through the agency of the 

 myceHum. Acton (1889) has demonstrated that carbohydrates and extract of 

 humus, etc., may be absorbed by the roots of ordinary green flowering plants and 

 assimilated. It is likewise probable that non-chlorophylliferous flowering plants, 

 may absorb similar organic substances, and supply themselves with carbohydrates. 

 In Dipodium the fungus coiild, therefore, obtain for the higher plant the car- 

 bonaceous constituents of the humus from which the starch would be manufac- 

 tured, and the less-oxygenated nitrogenous constituents of humus which would 

 be built up with the starch into proteid by the fungus, this proteid subsequently 

 being absorbed by the host-cytoplasm during the digestion of the endophyte. 

 The appearance of starch grains during the digestion of the fungus may be 

 due to the breaking up of the proteid into carbohydrate and nitrogenous com- 

 pounds of less complexity, or to the synthesis of starch by the host-cell directly 

 from the carbonaceous substances derived by the fungus from the humus. 



