220 SOUTH AFRICAN FLOWERING PLANTS. 



are seven or eight stamens adherent at the base (4). 

 (5) is the pistil, the ovary being cut open vertically to 

 show the ovule arising from the base, and three styles 

 and stigmas above. (6) is a ripe, three-cornered fruit 

 invested by the persistent calyx. (7) is the seed seen 

 in section, showing the embryo on the surface of the 



Fig. Sl.—Pohjc/'onum (Knot-grass). (For doscriplion, see text.) 



endosperm. It is the presence of a large quantity of 

 this " farinaceous " — that is, " starchy " — endosperm that 

 makes buckwheat so valuable for poultry, etc. 



There is a native species very much resembling it, 

 with slender flowering shoots, called P. serrula'tum. 



Ehubarb is a genus found in the northern hemi- 

 sphere, the species occurring in Eussia, Siberia, and 



