372 VARIOUS PLANT GROUPS 
120. The buckwheat family (Polygonacez). Examples: 
buckwheat (Fig. 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- 
gonacee. 
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 ocree,: 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 buckwheat 
the andrcoecium 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.? 
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. 
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, 
1Oc’re-a < L. a legging. Ll). 
2 Or-thot’ro-pous < Gr. orthos, straight. Symbolized by a straight 
line over the numerical sign, E1, 
