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BOTANY OF CROP PLANTS 



pericarp is hard or leathery. The single seed in each fruit 

 assumes the shape of the pericarp; the seed coat (testa) is 

 membranaceous, the endosperm is abundant and mealy, and 

 the embryo is straight or curved. 



Key to Pkincipal Genera 



Flowers subtended by involucres; ocreae wanting, Eriogonum. 

 Flowers not subtended by involucres; ocreae present. 

 Calyx six-parted (rarely four). 



Stamens nine (very rarely six), Rheum (rhubarb). 

 Stamens six, Rumex (dock). 

 Calyx five-parted (rarely four). 

 Achene much surpassing the calyx, Fagopyrum (buckwheat). 

 Achene enclosed by the calyx. Polygonum (bistort, persicaria, knot weed, 

 bindweed, etc.). 



RHEUM RHAPONTICUM (Rhubarb, Pie Plant) , 



Roots, Stems, Leaves, Flowers. — This plant is a perennial 

 from large, quite woody rhizomes which have a fibrous and 



Fig. III. — Rhubarb (Rheum) flower, external view, median lengthwise 

 section, and with perianth and stamens removed. (After Lilrssen.) 



well-developed root system. The rhizome is used in the 

 propagation of the plant. In the spring, a number of large 

 leaves are sent up from the underground stem, and, later in 



