286 BRITISH FLOWERING PLANTS chap. 



CiGENDIA 



Parts of the flower in fours. There are two British 

 species : C. filiformis, with broad, the other, C. pusilla, 

 with linear, calyx teeth. 



Eeythr^ea 



Parts of the flower in fives. There is no honey, but 

 the flower is sweet and juicy, and it would appear that 

 insects pierce the tissue and suck out the sap. They 

 only open in fine weather, and close again if it rains. 



E. Centaurium. — A variable species, the forms of 

 which are regarded by some botanists as distinct species, 

 while others consider them to be mere varieties. The 

 flowers are homogamous, but the stamens and pistil at 

 first bend away from, afterwards, however, approaching, 

 one another. Wilson ^ found them to be heterostylic, 

 with corresponding difierences in the pollen. This has 

 been confirmed by Loew. German botanists have not 

 altogether accepted this view, though they found that 

 the pistil varies in length. According to Kerner, the 

 life of the flower lasts five days. They open, according 

 to Warnstorf, from 5-7 a.m., and begin to close about 

 mid-day. 



Gentiana 



Blue, yellow, or red flowers, with the parts in fours 

 or fives. They have honey secreted at the base of the 

 ovary and of the corolla, and from the length of the 

 tube generally accessible to humble bees and Lepi- 

 doptera only. In many Gentians the leaves are so 

 arranged as to hold water, retaining it for some time, 

 during which it can be absorbed by special club-shaped 

 hairs. Some species are protected from browsing quad- 

 rupeds by a bitter sap. The stamens are adnate to the 

 corolla, projecting in the form of ridges, and thus divide 

 the hollow of the flower into four or five separate tubes. 



G. Pneumonanthe. — The flowers are protandrous. 

 They close at night and in wet weather. The 



^ Natiire, xviii. (Sept. 5, 1878). 



