98 



AN GIOSPERM AE— DICOTYLEDON ES 



Fig. 259. Menyanthes trifoliaia, L. (after 

 Warminfj). An isostylous flower from Julians- 

 haab, in Greenland, in longitudinal section 

 (X 3). 



average 26 yu, long and 50 /j, broad, while those of the short-styled form are 120 /a 

 long and 63 ^ broad. 



In the short-styled flowers I have examined at Kiel the stigma is situated in 

 the throat of the corolla, while in long-styled ones it projects several millimetres 

 from this. The anthers diverge in a swallow-tailed fashion, and their height is 

 of course inversely proportional to that of the stigma. Their pollen-covered 

 surfaces are directed inwards. Heinsius describes the extremely long stigmatic 

 papillae of the two forms as pretty much the same, but it seems to me that 

 there is a difference in size approximately proportional to that of the two kinds 



of pollen-grain. He also states that though plants 

 of the same kind are associated in groups, 

 legitimate crossing is frequent as indicated by 

 the size of the pollen-grains adhering to the 

 stigmas. 



Kerner and Warnstorf say that the flowers 

 are not only dimorphous, but also feebly pro- 

 togynous. According to the former, automatic 

 self-pollination can take place pseudo-cleisto- 

 gamously in the closed flowers. 



Visitors. — Sprengel observed humble-bees, 

 corresponding in size to the flowers. At Kiel 

 I have only seen the beetle Meligethes, while 

 Warnstorf only noticed small beetles and flies 

 at Ruppin. Heinsius saw the butterfly Pieris rapae L., skg., in Holland. In 

 Dumfriesshire Apis and a humble-bee have been recorded (Scott-Elliot, ' Flora of 

 Dumfriesshire,' p. 119). 



579. Limnanthemtun S. P. Gmel. 



Flowers dimorphous, with concealed nectar, secreted at five places between the 

 roots of the filaments. 



1889. L. nymphoides Hoffmgg. et Link (= Menyanthes nymphoides Z., and 

 Villarsia nymphoides 7ot/.). (Kuhn, Bot. Ztg., Leipzig, xxv, 1867, p. 67; Heinsius, 

 Bot. Jaarb. Dodonaea, Ghent, iv, 1892, pp. 72-6; Kerner, 'Nat. Hist. PI.,' Eng. Ed. i, 

 II, p. 171.) — Kerner states that as the flowers of this species wither the petals become 

 pulpy, the cell-sap exuding to form a thin surface layer which is particularly attractive 

 to flies. These visitors effect cross-pollination. Heinsius describes the large, bright 

 yellow, stellate corolla as possessing fringe-like appendages on the boundary between 

 its tube and limb. These are directed obliquely upwards and extend to the ovary, 

 completely closing the entrance of the flower. The long style is of the same breadth 

 as the short one, but about half as long again. The proportion is 28 : 20, while the 

 relative length of the corresponding stamens is 20 : 27. The bluntly triangular 

 pollen-grains are about 24-37 t^ in diameter in the long-styled form, and 43-6 fx 

 in the short-styled one. 



The flower-buds are submerged, raising themselves above the surface before 

 they open. When anthesis is over, the peduncle bends again, and the fruit ripens 

 under water. Heinsius often found pollen-grains from the opposite form on the 

 stigma, a proof that legitimate union takes place. 



