272 BRITISH FLOWERING PLANTS chap. 



other, L. nemorum, with small rotate flowers and 

 narrow calyx segments. 



L. vulgaris appears to be in special relation with 

 one species of bee — Macropis labiata. This insect does 

 not appear to exist where L. vulgaris does not occur. 

 Besides the usual large flowers there are other smaller 

 ones, slightly modified, so as to favour self-fertilisation. 

 The stem is sub-quadrangular, and the leaves pubescent 

 below, with black spots. 



L, Nummularia (Moneywort). — From the structure 

 of the flower the pollen must often fall on the stigma, 

 but, according to Darwin, it has little eff'ect, and Kerner 

 refers to the species as self-sterile. The plant is gla- 

 brous, with a quadrangular stem. 



L. thyrsiflora has protogynous flowers. 



Trientalis 



The parts of the flower are generally in sevens, 

 which is a very unusual number. There is no honey, 

 but a juicy fleshy ring surrounding the ovary, and, 

 bearing the stamens, is probably pierced by the insects 

 for the sake of the sweet juice. This and other similar 

 cases seem to indicate the manner in which honey may 

 have been gradually evolved. 



T. europaea is generally protogynous, but the plants 

 observed by Schulz in the Riesengebirge were homo- 

 gamous, or very slightly protogynous. When the 

 anthers open, an insect visiting the flower would touch 

 them on one side and the stigma on the other. The 

 pistil somewhat elongates while the flower is open, so 

 that eventually the stigma is raised a little above 

 the anthers. Finally, the flower closes, pressing the 

 anthers against the stigma, and thus, it would seem, 

 ensuring self-fertilisation. 



Glaux 



A small decumbent seaside plant, without any 

 corolla, the function of which is taken over by the 

 reddish calyx. Honey is .secreted, though only in small 



