POLYGONACE.i; 28 



3 



Inflorescences. — The inflorescences vary a great deal 

 within the family; in buckwheat they are panicled racemes, 

 in Polygonum spp., terminal or axillary spike-like racemes, 

 in Eriogonum spp., cymes, umbels or heads. The cyme is a 

 determinate type of inflorescence. In this type, the terminal 

 flower is the oldest and subsequent ones open in order from 

 the inside to the outside of the inflorescence (centrifugal open- 

 ing of the inflorescence). In the head type of inflorescence, 

 so well exemplified by the dandelion or sunflower, the flowers 

 are crowded on the receptacle; the stalk of each flower is 

 very short or entirely absent; it is an indeterminate type. 



Flowers. — The flowers are small, mostly perfect, rarely 

 dioecious or monoecious, and radially symmetrical. In 

 the genus Eriogonum, the flowers are subtended by a five- to 

 eight-toothed involucre. The calyx consists of two to six 

 segments which are below the ovary and free from it; the 

 segments are in one or two series, often imbricated (over- 

 lapping) , and the inner or both series are petaloid (resembling 

 petals). There are no petals. The stamens vary from two 

 to nine; in perfect flowers, they are attached near the base 

 of the calyx, while in staminate ones, they may be crowded 

 on a central disk; the filaments are filiform, mostly distinct 

 but sometimes united in a ring at the base, and commonly 

 dilated at the base; the anthers possess two cells, and are 

 longitudinally dehiscent. The pistil is solitary. The su- 

 perior ovary is one-celled, three-angled or. compressed, rarely 

 four-angled, and usually sessile; the styles are most frequently 

 three in number, rarely two or four, and attached to the apex 

 of the ovary; the stigmas are capitate (head-shaped) or 

 tufted, and sometimes two-cleft. Within each ovary there 

 is a single ovule. 



Fruit. — The fruit is a three-angled (rarely four-angled) 

 achene, about which is frequently the persistent calyx; the 



