208 BOTANY OF CROP PLANTS 



ous ocreae. The flowers are on short, jointed pedicels and 

 occur in fascicles, each of which is a raceme; the entire 

 inflorescence is paniculate. The flowers (Fig. iii) are small, 

 greenish white and perfect; the calyx is six-parted, persistent, 

 and becomes enlarged somewhat in the fruit (Fig. 113); 

 there are nine stamens; the ovary is three-angled and bears 

 three short, recurved styles, with large stigmas. 



— ,win^ 



peaistenv' ''' 

 cd/yx lobe 



Fig. 113. — Fruit of rhubarb (Rheum rhaponticum) . A, external view; B. 

 cross-section. X S. 



Self-pollination is prevented to a large degree by the matu- 

 ration of anthers before the stigmas. Stigmas of flowers 

 below on the inflorescence receive pollen from the anthers of 

 younger flowers borne above them. Pollen is disseminated 

 by wind, insects, and gravity. 



Fruit. — Rhubarb fruit (Fig. 113) is an achene surrounded 

 at the base with the persistent remains of the perianth; it has 

 three broad, thin wings which are traversed by a longitudinal 

 nerve running near the margin; it is tipped by a small per- 



