The Nutrition of Mycorrhiza Plants: Calluna Vulgaris

Abstract

1. An account is given of the formation and seasonal development of mycorrhiza in Ling (Calluna vulgaris). 2. Digestion of the intracellular complex of mycelium in the mycorrhiza cells is recorded for the first time and the cytology of the process is described. 3. Knowledge of the distribution of the endophyte in the shoot tissues has been extended, and is confirmed by experimental work on cuttings struck in sterilised sand under controlled conditions. The endophyte has been recovered and identified from the shoot. 4. The results thus obtained are compared with those described by Christoph, whose observations are interpreted in the light of the account now given of the formation of "suppressed mycorrhiza" in roots of cuttings, and also in those of seedlings and mature plants when certain conditions exist in the rooting medium. 5. It is pointed out that the "obligate relation" in Calluna is associated with infection and seedling development and not with mycorrhiza formation and growth. The view is expressed that plants would probably grow quite well without mycorrhiza could seedlings be raised free from infection. In nature, the formation of mycorrhiza in all roots is the rule; the activities of the endophyte and its digestion products are presumably related to the nutrition of the plant and may be correlated with its growth in particular soils. 6. The evidence for exchange of nutritive material is stated and examined. The view has been reached that such exchange exists, with a "balance of profit" on the side of the vascular plant. 7. In view of its application to cases for which experimental data are not available, it is suggested that the term "symbiosis" as applied to mycorrhiza plants should be used in the older sense defined by de Bary.