POLYGON ACE AE 341 



766. Polygonum L. 



Literature. — Herm. Miiller, ' Fertilisation,' p. 516 ; Knuth, ' Bl. u. Insekt. a. d. 

 nordfr. Ins.,' pp. 127-8; Meehan, Proc. Acad. Nat. Sci., Philadelphia (Pa.), (1889) 

 1890. 



Flowers mostly homogamous or protandrous, belonging to classes Po, EC, and 

 C. Perianth generally petaloid, and flowers frequently aggregated into conspicuous 

 inflorescences. Nectar either secreted in the base of the flower or absent. Some- 

 times dimorphism. Gynodioecism or gynomonoecism frequent. Meehan says that 

 numerous species, e.g. P. Persicaria L., P. aviculare Z., and P. Hydropiper L., bear 

 cleistogamous flowers. 



Hermann Miiller states that ' The species of Polygonum, like those of 

 Geranium, show clearly how with conspicuousness and abundance of honey the 

 number and variety of visitors increase, and how, as the likelihood of cross-fertiliza- 

 lion is thus increased, the possibility of self-fertilization becomes less important ; the 

 converse is also clear. But they show at the same time that the abundance of 

 a plant is in no way determined alone by the certainty of cross-fertilization ' (op. cit., 

 p. 516). 



2469. P. Fagopyrum L. (= Fagopyrum esculentum MoencK). (Hildebrand, 

 ' D. Geschlechts-Vert. b. d. Pfl.,' p. 40; Jordan, K. F., Ber. D. bot. Ges., Berlin, v, 



Fig. 350. PolygortuTn Fagopyrum^ L. (after Herm. Miiller). (r) Long-styled, and (2) short-styled 

 flower, after removal of two perianth leaves. a, anthers; M, nectary; st^ stigmas. 



1887; Herm. Miiller, 'Fertilisation,' pp. 509, 516; Knuth, 'Bl. u. Insekt. a. d. 

 nordfr. Ins.,' pp. 129, 166-7; Kirchner, 'Flora v. Stuttgart,' p. 213; Schulz, 

 ' Beitrage,' II.) — The flowers of this species are dimorphous, with exposed to half- 

 concealed nectar. They are white or reddish in colour, and crowded together so as 

 to be highly conspicuous ; in consequence of this, their honey-like odour, and great 

 richness in nectar, insect-visits are extremely numerous. Cross-pollination by means 

 of heterostyly is therefore ensured, while automatic self-pollination is only occasionally 

 possible. 



The diameter of the flower is about 5 mm. Eight (sometimes nine) large yellow 

 nectaries, bound together by a cushion-like swelling, are situated at the base of the 

 ovary : their abundant secretion always attracts swarms of insects. 



The long stamens and pistils are fully 3 mm. long, the shorter ones almost 

 2 mm. In the long-styled form, therefore, the widely exserted stigmas project 

 2 or 3 mm. beyond the anthers ; in the short-styled form they are about the level 

 of the middle of the filaments. The pollen-grains of the latter form are larger than 



