. The classification of flowering plants. Plants. PYROLACEAE 433 Monotropoideae the dehiscence is by slits and the pollen is simple. The corolla and stamens are often inserted at the edge of a nectar-secreting disc, which is sometimes represented by separate nectaries or is rarely completely absent. The fieshy ovary bears a simple columnar style; in some genera of Monotropoideae it is unilocular except at the extreme base, but generally the septa are wanting only in the upper part of the chamber. The ovary-cavity is almost filled by the thick fleshy placenta, the surface of which is crowded wi
. The classification of flowering plants. Plants. PYROLACEAE 433 Monotropoideae the dehiscence is by slits and the pollen is simple. The corolla and stamens are often inserted at the edge of a nectar-secreting disc, which is sometimes represented by separate nectaries or is rarely completely absent. The fieshy ovary bears a simple columnar style; in some genera of Monotropoideae it is unilocular except at the extreme base, but generally the septa are wanting only in the upper part of the chamber. The ovary-cavity is almost filled by the thick fleshy placenta, the surface of which is crowded with ovules. The minute seeds have a delicate loose testa enclosing a central nucleus consisting of an oily endosperm and a few-celled undifferentiated embryo. Pyrola, the largest genus (15 species), extends into the. Fig. 210. A. Floral diagram of Pyrola. B. Flower of P. uniflora, enlarged: two petals have been removed to shew the glandular disc, d. C. Transverse section of base of ovary of Monotropa Hypopitys. D. Similar section above the middle; both enlarged. E. Median portion of the seed of M. Hypopitys, much enlarged; e, embrvo; n, endosperm; t, loose seed-coat. (A after Eichler; B-E after Drude.) Arctic zone, and southwards into the Himalayas and the mountains of Mexico; four species are British. Monotropa, with three species, has almost as wide a distribution; the British species, M. Hypopitys, occurs in Europe, Siberia, Japan and in the Xew World from Canada to Mexico; of the allied genera seven are North American and one is Himalayan; Sarcodes, a monotypic genus in the Sierra Nevada of California, sends up a fleshy spike of brilliant red flowers through the melting snow^. P}Tolaceae are closely allied to Ericaceae from which the}- are distinguished by incomplete septation of the ovary and the un- differentiated embr^'o. They may be derived from an Ericaceous stock with free petals (such as are found in Ericaceae in Ledum and allied genera) in which the shrubby habit has
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