Domatia

These small structures in nerve axils at the underside of leaves have given food to various theories and have been nonetheless in phytographic and taxonomic neglect almost from the beginning. That was in 1887, when the Swede A.N. Lundstroem published an extensive paper, in which he explained domatia as structures intended to accommodate mites – hence the word acarodomatia – which latter would in turn benefit the plant by cleansing the leaves from fungus spores. Lundstroem arrived at this hypothesis on the strength of ideas current in that time, about the existence of symbiotic relations between ants and plants; it was in the heydays of teleology. A closer investigation left little of the illusions about mutual benefit between ants and plants, but such critical interest was never focused on the supposed relation between mites and plants. Recently I could grow a few domatia-bearing species under acari-free conditions; the plants with their domatia did as well as in the open. Yet it is hard to prove that Lundstroem was wrong, but a combination of the experiment, the wellknown fact that domatia are inhabited by acari as often as not, and the origin of the hypothesis make if very unlikely that mites will creep into domatia for other reasons than a natural preference for shelter in small holes. All other (physiological) explanations are unconvincing, too, and so for the time being an explanation is lacking – provided that such an explanation would be necessary.