288 



BRITISH FLOWERING PLANTS 



about the species is that while it is annual in the plains, 

 in Alpine districts it becomes biennial.-^ 



Chlora .(Yellow-wort) 



The calyx and corolla are eight-lobed. The flowers 

 produce no honey. 



C. perfoliata. — The flowers close at night. The 

 leaves are glabrous and connate, forming a smooth 

 collar round the stem, which creeping insects cannot 

 get over. 



Menyanthes (Buckbean) 



Honey secreted by the base of the ovary. Flowers 

 generally dimorphous. 



M. trifoliata. — The upper surface of the corolla is 

 clothed with beautiful white filaments. According to 

 Knuth these render the flower more conspicuous, and 

 also serve as a protection against rain and unwelcome 



Fig. 187. 



Fig. 188. 



Fig. 187. — Menyanthes trifoliata. Short-styled form, after tlie removal of the froDt 



part of the corolla aud front stamens (nat. size). 

 Fig. 188. — long-styled form (as before). 



po, pollen from the stamens of each form ( x 70) ; s, papillffi of the stigma of 



the two forms ( x 4). 



intruders. I am not satisfied that this is a sufficient 

 explanation. This curious and beautiful flower is 

 dimorphous in some places and not in others. Sprengel 

 knew only the homomorphous form. Warming in 

 West Greenland plants found the stamens and pistil of 



' Grisebaoh, Die Vegetation der Erde. 



