Ecology and Morphology of Pterospora andromedea

Pterospora andromedea Nutt. is the only species of this North American genus. A dot map prepared from herbarium specimens showed that the species has a bicentric distribution confined to cool temperate forests of eastern and western North America. The plant is characteristic of shady habitats and moist podzolic soils. It is sparsely distributed in the plant associations studied by the writer and is even less common in most other parts of its range. Material for a study of the ecological life history of Pterospora was obtained in eastern Washington and adjacent Idaho. 2. After attaining maturity, seeds remain alive for 3-9 weeks. Thirty-three treatments used in an effort to induce germination failed. Established seedlings have been observed in nature. The species is both annual and perennial. 3. Chromosome counts during the first division of the microspore mother cells showed the diploid number to be 16. 4. Embryo-sac development is of the Polygonum type. Various abnormalities including the bisporic type of embryo-sac development were seen. The endosperm is cellular; embryogeny conforms to the Aglaonema variation of the Caryophyllad type. Not more than 4-5% of seeds in a capsule were found to be exembryonate. The development of the seed and its wing has been studied in detail. 5. Pterospora has a dense, spherical root mass from which long lateral roots producing shoots at various intervals are given out. The roots have no organic connection with any other vascular plant. There is an unbroken mycelial sheath around each root so that Pterospora does not make direct contact with the soil. The mycelium consists of septate hyphae the cells of which may be either uninucleate or binucleate. Attempts to isolate and identify the fungi were unsuccessful. 6. The anatomy of root, stem, leaf, and flower has been studied. There are extremely few stomata per unit area of leaf and stem. Spectrophotometric and paper chromatographic studies revealed the presence of β-carotene, but the chlorophylls were found to be absent. The marked reduction in leaves and in number of stomata per unit area appears to be associated with the absence of chlorophyll which, in its turn, is correlated with the plant's apparent dependence for all its nutritional requirements on the fungi ensheathing its roots. 7. On the basis of the available evidence it has been concluded that Pterospora is not a "root parasite" or a "saprophyte" as commonly stated but is parasitic on the root fungi.