346 



A NGIOSPERMAEDICOTYLEDONES 



which the two styles project about i^ mm., while the two anthers are situated abou^ 

 a mm. below the mouth of the flower. 



Schulz observed gynomonoecism or gynodioecism occurring frequently or 

 sometimes even exclusively. 



The terrestrial form (var. terrestre Leers) possesses short hairs on the stalks^ 

 which secrete a viscid fluid serving as a protection against creeping insects; the 

 aquatic form (var. natans Moench) is glabrous, the surrounding water giving access 

 to none but flying insects. 



Visitors. Knuth (Fohr) observed the following. 



A. Diptera. (a) Muscidae : all po-dvg. : i. Aricia incana Wied. i ; 2. Coenosial 

 tigrinai^. $; 3. Lucilia sp. ; 4. Scatophaga merdaria i^. ; 5. S. sp. {V) Syrphidae\ 

 6. Eristalis sp., po-dvg. B. Hymenoptera. Apidae : 7. Apis melUfica Z. g.j 

 po-cltg. and skg. ; 8. Halictus cylindricus F. 5, po-cltg. C. Lepidoptera. Rhopalo 

 cera : 9. Coenonympha pamphilus L., skg. 



The following were recorded by the observers and for the localities stated.- 



MacLeod (Flanders), the hover-fly Eristalis tenax Z. (Bot. Jaarb. DodonaeaJ 

 Ghent, vi, 1894, p. 375). Scott-Elliot (Dumfriesshire), a Muscid, a hover-fly, and 

 several Dolichopodids ('Flora of Dumfriesshire,* p. 149). 



2475. P. Persicaria L. (Herm. Muller, 'Fertilisation,' p. 512; Knuth, 'B13 



u. Insekt. a. d. nordfr. Ins.,'| 

 pp. 128, 166; Verhoeff, 'Bl 

 u. Insekt. a. d. Ins. Nor- 

 derney ' ; Schulz, ' Beitrage ' ^ 

 Kirchner, * Flora v. Stuttgart, 

 pp. 216-17.) The flowers ol 

 this species belong to classes 

 C to EC. They are small, 

 odourless, white or reddish in 

 colour, rather poor in nectar, 

 and united into crowded inflorescences ; a certain conspicuousness is thus attained, 

 and insect-visits are fairly frequent; cross-pollination is therefore possible, though 

 automatic self-pollination often takes place. There is a nectary at the base of 

 each of the eight stamens, but the secretion is scanty. Three stamens are usually 

 reduced or entirely absent; but not infrequently flowers occur with six, seven, or 

 eight fully developed ones. The two (more rarely three) stigmas mature simul- 

 taneously with the anthers, and are at the same level. At first the perianth leaves 

 and the five fertile stamens alternating with them bend so far outwards that the 

 stigmas are not touched. When more than five stamens mature they bend towards 

 the middle and bring about automatic self-pollination by coming into contact with 

 the stigmas. But even in flowers in which only five stamens mature, automatic 

 self-pollination takes place later, and this is eff"ective, as almost all flowers set fruits. 



When visited by insects, the flowers may be self- or cross-pollinated with equal 

 facility, as they are so small that the insect's head, on entering, must touch stigmas 

 and anthers at the same time. Should the insect insert its head only once, cross- 

 pollination is effected, but repeated entrances bring about self-pollination. 

 Visitors. Herm. MUUer gives the following list for Westphalia. 



(I) 



Fig. 353. PolygonutM Persicaria^ L. (after Herm. MUller) 

 A flower with five stamens. (2) Pistil. (3) A flower with seven 



stamens. a and a', outer and inner stamens; a\ vestigial stamen ; 

 , nectary ; of, ovary ; st, stigmas. 



i| 



