MYCORRHIZAL SYMBIOSIS IN APLECTRUM, CORALLORHIZA AND PINUS

When plants of different types are closely crowded together or anatomically engaged, in addition to the ensuing competitions, several special relations including immunities, antagonisms, toxicities, parasitism, or symbiosis may arise. A secretion by one plant which inhibits the growth of a neighboring organism, such as the substance found in the tissues of orchids by NOEL BERNARD which limits the growth of the hyphae of endophytic fungi, results in an immunity. Similar antagonisms exist between some fungi growing together in the soil in which a secretion from one limits the growth of the other (11). This constructively defense mechanism varies widely. In one instance described by STOLLER (21) Psalliota campestris produces a diffusible oxidizing substance, acting as a quinone which protects the mushroom against microorganisms producing sulphides. The action of the " humoral " secretion in such cases is to be distinguished from toxicity by the fact that in the first case the secretion simply blocks some of the processes of cell-metabolism but does not destroy the mechanism; in toxic action a theoretical secretion causes irreversible and fatal changes in the cytochemical set-up of living cells of the organism affected. In parasitism, in addition to possible anatomical and cytochemical damage, a fatal extraction of nutritive material may ensue. Further distinction between parasitism and symbiosis will be made in the following pages. A much heightened interest in the bacteriostatic secretions of molds, of which penicillin is the most notable because of its sterilizing action in surgery, now prevails. This secretion specifically inhibits the growth of grampositive bacteria but does not destroy them; secretions such as patulin exert similar. action on both gram-positive and gram-negative bacteria [see also BURGESS (2)]. Scope of the present paper