The diagram is generally Sn, Pn, An + n, Gn, in which n is 4 or 5. To this may be added, that the corolla is in most cases gamopetalous, but in some (especially Pyrolaceæ) perfectly polypetalous; and that the anthers usually open by pores, and often have two horn-like appendages (hence the name “Bicornes”) (Figs. [545], [546]); frequently the two halves of the anther are also widely separated from each other at the upper end, so that the pores are placed each one at the end of its own tube (Fig. [546]); the pollen-grains in the majority are united into tetrads (Fig. [542] D).—The flowers, as a rule, are pendulous and borne in racemes, coloured (red or white), but odourless. When the fruit is a capsule, the placenta with the seeds attached persists as a central column. A mycorhiza occurs on many.
The majority of plants belonging to this family inhabit cold and temperate countries, or high mountains in tropical regions; they prefer cold and dry or damp places (bogs, heaths, etc.). Plentiful in N. America.
Order 1. Pyrolaceæ. Perennial herbs; petals most frequently quite free from each other, and falling off singly after flowering; the anthers are without appendages, and open by pores (Fig. [544]), or by a transverse slit. The placentæ are thick. The seeds in the capsule-like fruit (loculicidal dehiscence) are exceedingly small and light, they have a sac-like testa which loosely envelops them, an oily endosperm, and an extremely simple embryo, which consists only of an ellipsoidal, cellular mass, without cotyledons or differentiation into plumule and radicle.
Pyrola (Winter-green) is green, and has also large evergreen foliage-leaves. The flowers, 5-merous, are most frequently borne in racemes without a terminal flower; the anthers are extrorse in the bud with the pores in the lower portion (Fig. [544] A), but they become inverted at a later period, so that the pores open at the top (Fig. [544] C). P. uniflora has a single, terminal flower; it winters by its roots, producing from these in the spring aerial, quite unbranched shoots. Chimaphila umbellata.
Fig. 544.—Pyrola minor: A portions of a young flower; B the stigma; C portions of an older flower (longitudinal section).
Monotropa (Yellow Bird’s-nest) is very pale yellow, without chlorophyll, succulent, and has only scale-like leaves closely pressed upon the stem; it is a saprophyte. The raceme has a terminal flower, and is pendulous before flowering. The anthers open by a semicircular, transverse cleft. M. hypopitys reproduces chiefly by root-shoots.
About 30 species, especially N. Europe, N. America, and N. Asia.
Order 2. Ericaceæ. The flower (Fig. [545]) is hypogynous, the median sepal posterior; corolla, gamopetalous; the stamens are generally 2-horned, and the fruit is a capsule, less frequently a berry or drupe. At the base of the ovary is a nectar-secreting disc (Fig. [545] B). This order comprises shrubs or undershrubs (rarely small trees), which are evergreen, and as a rule have densely crowded leaves.
1. Ericeæ, Heath Group. Flowers most frequently 4-merous (S4, P4, A4 + 4, G4, united in a 4-locular gynœceum), rarely 5-merous. The withered corolla persists after flowering. The leaves are most frequently acicular, opposite or verticillate; the buds are without scales. The fruit is a capsule.—Calluna (C. vulgaris, Ling) has a deeply 4-cleft corolla, which is less than the coloured calyx; capsule with septicidal dehiscence.—Erica (about 420 species; E. tetralix, Cross-leaved Heath) has a tubular or bell-shaped, 4-dentate corolla, which is much longer than the calyx. Capsule with loculicidal dehiscence.—Pentapera.