CAMPANULACEAE 17 



ness of which is enhanced by their blue colour. The delicate narrow epigynous 

 corolla (4-6 mm. long) has a funnel-shaped limb and a relatively long and very 

 narrow tube. Before the flower opens the throat of the corolla is completely filled by 

 the five anthers, which are borne on slender filaments. The end of the style is 

 capitate, and beset with erect, mostly unicellular, hairs swollen at their bases. At 

 this stage it is below the whorl of anthers. The style now quickly elongates, and 

 presses strongly against the dehiscing anthers, the resistance of which being too great 

 for it to overcome often causes it to be thrown into a curve. Still further elongation 

 throws the style into a state of increased tension, which is finally relieved by the 

 opening of the corolla. The end of the style now suddenly forces its way through 

 the anthers, carrying off the pollen on its hairs, and protrudes for a considerable 

 distance from the entrance of the flower. At first the pollen adheres so closely to the 

 sweeping-hairs that it cannot be removed by stroking with the fingers, but very soon 

 these hairs begin to contract at their bases so that the pollen can be easily detached. 

 This is usually eff'ected by insect visitors, and proliferation of the stigmatic tissue at 

 the end of the style now begins, causing this to split and develop into an obscurely 

 3-lobed stigma, which ultimately develops into three very short white stigmatic 

 branches. As by this time all the pollen of the flower has been removed, crossing by 

 insect visitors is the only possible means of fertilization, for automatic self-pollination 

 is out of the question. The individual flowers of an inflorescence are in different 

 stages of anthesis, though the stage in which pollen is present lasts for a much 

 shorter time than that during which the stigmas are receptive. The semi-transparent 

 corolla-tube is half full of nectar, which is sucked by insect visitors. The interesting 

 specializations in which Trachelium differs from Campanula and similar genera are 

 the following. — 



Sweeping away of the pollen from the dehisced anthers by means of sweeping- 

 hairs on the end of the style. Successive protrusion of pollen and stigma outside the 

 flower. Reduction in size and narrowing of the corolla, with nectar concealed in 

 a tube only accessible to butterflies, the proboscis of which is at the same time guided 

 to it. Aggregation of very numerous small flowers into a flat-topped inflorescence, 

 enabling many of them to be visited and pollinated in a short time. These adapta- 

 tions obviously make crossing by insects so certain that the species can well afford 

 to dispense with the possibility of automatic self-pollination. 



Visitors. — Delpino observed butterflies (various sp. of Pieris, skg.), and a small 

 bee (Halictus sp., po-cltg.). 



515. Wahlenbergia Schrad. 



This agrees with Campanula, but Schonland says that the pollen-grains on the 

 style are held fast by the secretion of a sticky fluid. 



1735- W. hederacea Reichb. (Willis and Burkill, ' Fls. and Insects in Gt. 

 Britain,' Part I, p. 263.) — Willis and Burkill have investigated this species in Central 

 Wales, and describe the corolla of the erect tubulo-campanulate flower as about 

 10 mm. long, with an opening 3-4 mm. wide. It is odourless, and pale-blue in 

 colour, traversed by darker veins. The stamens do not possess the broad base and 

 slender distal region seen in the species of Campanula, but the filaments gradually 



