Part 120. The buckwheat family (Polygonaceae). Examples: buckwheat (Fig. 22) and rhubarbs (Fig. 112 and Fig. 163).

See pages 412, 413 for formulas of Rheum, Fagopyrum, and Polygonaceae.

The stems of plants belonging to the buckwheat family are commonly swollen at the joints, and have above each node a thin tubular sheath formed by the coalescence of the stipules. These sheaths are called ocreoe,1 and the plants or leaves are said to be ocreate.

1 Oc're-a - L. a legging. Lj).

The parts of the flower are commonly in threes although there are some curious departures from the type. Thus in buckwheat (Fagopyrum) there are five sepals as against the six-leaved perianth of rhubarb (Rheum), but we may regard the missing sepal as represented by a bractlet which is absent in the other inflorescence. Again, the six outer stamens of rhubarb are to be regarded as three pairs, each pair formed from the division of one stamen into two; while in buckwheat the androecium is similar except that one of the outer stamens has remained undivided, thus giving but eight in all. That there are three carpels is shown clearly by the three distinct styles, though there is but one cavity from the base of which arises a single ovule. This ovule differs from the others we have studied in having the micropyle opposite to the funicle, that is to say, in being straight or orthotropous.2

2 Or-thot'ro-pous - Gr. orthos, straight. Symbolized by a straight line over the numerical sign, Ei.

The family consists mostly of herbs with a watery juice which is often peppery and sometimes pleasantly acid, without reservoirs of volatile oil; having stems often swollen at the joints; leaves ocreate; styles two or three, distinct; ovary containing a single, orthotropous ovule; and the fruit an achene.

Part 121. The Buckwheat Order

Part 121. The buckwheat order (Polygonales) which contains only the above family, may be contrasted with the previous orders as having mostly paniculate inflorescences of small, regular, perfect, hypogynous flowers, with the perianth, leaves, and stamens distinct and alternate, and the ovary with but one cavity and one ovule.

The formula of Polygonales is given on pages 412, 413.