POLYPETAL^— VIOLACE^ 129 



filaments (/) are very short. The filament of each of the two 

 anterior stamens sends a slender elongated process or appendage 

 (ap) into the spur of the anterior petal. The green spots at 

 the ends of these two appendages secrete honey, and are the 

 nectaries. Carpels (fig. 158-6) three, superior, combined. Ovary 

 {pv) one-chambered, with three parietal placentas which bear 

 many ovules. Style {si) one, club-like, with a stigma in a pit 

 (cK) On the anterior surface of its summit (s). Fruit (fig. 158-4) 

 a capsule splitting down the dorsal sutures. The three valves 

 contract and jerk out the smooth seeds. Seed (figs. 158-7-8) 

 endospermic, with a lump {c, cd) near the micropyle. Pollina- 

 tion. — The anthers dehisce towards the gynaecium at the same 

 time as the stigma ripens. At first sight it appears that self- 

 pollination is inevitable ; and, indeed, self-pollination does take 

 place in the whitish-yellow small-flowered variety of the Pansy 

 ( V. tricolor var. arvensis). But in the large-flowered variety of 

 Pansy, which possesses variegated flowers, self-pollination is 

 hindered by a very neat mechanism. The stigma-cup has a 

 little shutter or flap (fig. 158-5, v) hinged on to its lower edge, 

 A bee visiting the flower alights on the anterior petal, and, in 

 order to sip the honey, it must push its tongue into the spur of 

 the petal. In so doing, the tongue necessarily passes along the 

 hairy groove between the stigma and the anterior petal. The 

 pollen collects in this groove. Consequently, when the bee 

 alights, its tongue first rubs against the stigma and drags open 

 the " shutter," so- that any pollen previously present on the 

 bee's tongue is rubbed into the stigma-cup. As the tongue is 

 pushed farther towards the honey it comes now for the first 

 time into contact with the pollen belonging to the flower itself; 

 and in this way the tongue becomes coated with the flower's 

 own pollen. When the bee has obtained some honey and pro- 

 ceeds to withdraw its tongue, the backward movement of the 

 latter closes the 'shutter of the stigma-cup, and thus prevents 

 the pollen of that flower from being rubbed into the stigma-cup. 

 In the large blue or variegated flowers of the large-flowered 

 variety of Pansy, the honey is so deeply placed (because the 

 spur is long) that it can be reached only by insects with long 

 tongues : these flowers are pollinated chiefly by bees and 

 humble-bees. On the other hand, in the small yellow or 

 yellowish-white flowers of the other variety of Pansy the honey 

 is more easily accessible ; consequently these flowers are visited 



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