No. 22.— Family POLYGONACE^. (Buckwheat 



Fam.) 



(i) Genus Polygonum. (Knotweeds.) 



From two Greek words meaning " many " and " knees," because of the jointed stems. 



Flowers, in clusters. Corolla, lacking. Calyx, five- (rarely 

 four-) parted, mostly greenish-white with colored 

 margins, more or less corolla-like in appearance, per- 

 sistent. Stamens, usually eight, rarely five, and in 

 No. i (P. arifolium) six. Styles or stigmas, three, 

 (two in No. i). Seed-cases, free, one-celled, one- 

 seeded. 



Leaves, simple, alternate, entire. Stipules, (ocrese) in the 

 form of sheaths around the stem at the swollen joints. 



Fruit, enclosed, or nearly enclosed, by the calyx, one- 

 celled. Seed, one, flattened or triangular. An 

 achene. 



All herbaceous. 



GUIDE TO THE SPECIES. 



(a) Stems prickly. 



(d) Leaves halberd-shaped. Stamens six, styles two. 

 (i) Halberd-leaved Tear-Thumb (P. arifolium, L.). 

 (b) Leaves arrow-shaped. Stamens mostly eight, 

 styles three. 



IS7 



