372 VARIOUS PLANT GROUPS 



120. The buckwheat family (Polygonaceae). Examples; 

 buckwheat (Pig. 22, page 29) and rhubarbs (Fig. 112, 

 page 104, and Fig. 163, page 170). 



See pages 412, 413 for formulas of Rheum, Fagopyrum, and Poly- 

 gonaceae. 



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 ocrece,^ and the plants or 

 leaves are said to be ocreate. 



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 ab- 

 sent 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 l^uckwheat 

 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 oi)posite to the funicle, 

 that is to say, in being straight or ortJtotropous.- 



The family consists mostly of herbs ivith 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. 



121. The buckwheat order (Polygonales) which con- 

 tains 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, 



' Oc're-a < L. a legging. LJ.). 



^ Or-thot'ro-pous < Gr. orthos, straight. Symbolized by a straight 

 line over the numerical sign, Ei. 



