The structure and physiological significance of the root-nodules of Myrica gale

The peculiar nodule formations on the roots ofMyrica gale were first described and figured by Brunchorst in 1886, who stated that they were caused by an inhibiting fungus with septate hyphæ and terminal spores. Möller in 1890 placed this fungus in the group Frankia, naming itFrankia Brunchorstii , and considered it to be closely related to a similar fungus in Alder nodules. In 1902 Shibara stated that the fungus is found exclusively in a peripheral sub-cork layer of tissue, one to three cells thick, and because of its peculiar ray-branching and club-shaped spores, it belongs to the group Actinomyces. Peklo in 1910, working on greenhouse-grown plants, supported Shibata’s view. Roots ofMyrica gale were obtained for this investigation from plants growing wild in Wales, Ireland, and the North of England, and from cultivated plants growing in the Chelsea Physic Gardens. In all cases the roots were found to possess nodules of varying size. The young nodules are from 2-3 mm. long and 0·8-1 mm. broad, but these by branching form “clusters,” sometimes as large as a nutmeg, and surrounded by peculiar rootlets which grow out through the end of each nodule or branch. The branching is associated with the outgrowth of lateral roots, and is not due to dichotomy of the apical meristem of the root as is the case in the nodules of Cycas, Alder, and Elæagnus.