1736 



A TEXTBOOK OF THEORETICAL BOTANY 



POLYGONALES 



The Polygonales are Archichlamydeae which are essentially herbaceous 

 plants, there being very few shrubby or arborescent types. The order is 

 closely related to the Centrospermae on the one hand and the Piperales on 

 the other. It contains the single family Polygonaceae and hence the 

 characters of the family and of the order are the same. 



The most characteristic feature is the peculiar sheathing membrane 

 attached to the node, which is called an ochrea (see Chapter XXII). It 

 clasps the stem above the leaf base and takes the place of stipules in pro- 

 tecting the bud during growth. The flow^ers are hermaphrodite, small and 

 actinomorphic and are usually produced in large numbers on a compound 

 inflorescence. The sepals vary from three to six and often enlarge and 

 become membranous in the fruit; petals are absent. 



The stamens vary from six to nine. The ovary is superior, composed 

 of three or sometimes two united carpels, but it is unilocular and has a single 



Fig. 1613. — RiiiJiex acetosella. 

 Sheeps' Sorrel. Flowering 

 shoots. 



Fig. 1 6 14. — Rheum. 

 Rhubarb. Part of an 

 inflorescence with 

 fruits. 



