136 ANGIOSPERMAE—DICOTYLEDONES 



of the dark-blue flowers, which are almost hidden by the leaves, is partly compensated 

 for by their powerful fragrance. The corolla is whitish in the middle, the white patch 

 on the lower (spurred) petal being traversed by dark-blue veins, which converge to 

 the opening of the spur, and serve as nectar-guides. The end of the style — which 

 bears the stigma — is dilated distally, bent down like a hook, and at some little 

 distance from the lower petal. MacLeod states that a fluid is secreted in the stigmatic 

 cavity, a drop of it being pressed out when an insect pushing into the spur touches 

 and raises the stigma. This drop moistens the head of the insect and prepares it 

 for the reception of the dry, white, smooth pollen, of which the separate grains are 

 about 44 /ti long and 25 /a broad. 



According to Hildebrand and Kerner, the lobe on the under-side of the 

 stigmatic cavity is covered with pollen when an insect visitor pushes its proboscis 

 into the flower, and when this is withdrawn the lobe is pressed up against the head 

 of the stigma so as to introduce the pollen into its cavity. 



Visitors. — Bees are the most important visitors. Sprengel depicts the honey-bee 

 as the pollinator on the title-page of his ' Entdeckte Geheimnisse ' ; and as a matter 

 of fact it is the most frequent visitor of this violet. Long-tongued bees have also 

 been observed — especially by Hermann Miiller — sucking nectar and effecting cross- 

 pollination. This may also be regularly brought about, though more rarely, by 

 Bombyliidae and butterflies (Vanessa, Rhodocera), which are attracted by the pleasant 

 odour and suck the nectar. Cross-pollination is essential to the chasmogamous 

 flowers, for Sprengel's experiments long ago proved that no fruits are set if insects 

 are excluded. Short-tongued humble-bees occasionally bite through the spur and 

 steal the nectar (Schulz). 



Kirchner states that — should insect-visits fail — cleistogamous flowers are developed 

 on the runners during August. These are axillary, with peduncles 3-5 cm. long, 

 and are bent downwards, sometimes even penetrating the loose soil. Within the 

 closed calyx there are five small pale petals folded as in a bud, five stamens with 

 small non-dehisced anthers, the pollen-grains of which send out tubes that penetrate 

 the stigma. These cleistogamous flowers are fertile : their capsules bury themselves 

 in the earth — when this is loose enough — and there ripen. 



The following insects have been observed by Hermann MuUer (H. M.) in 

 Westphalia, by Buddeberg (Budd.) in Nassau, and by myself (Kn.) in Schleswig- 

 Holstein. — 



A. Coleoptera. NitiduUdae: i. Meligethes (H.M.). B. Diptera. Bombyliidae: 

 2. Bombylius discolor Mikan, skg. (H. M.). C. Hymenoptera. Apidae : 3. Andrena 

 fulva ScAr. 5, vainly skg. (H. M.) ; 4. Anthophora pilipes F. J, skg. (H. M.) ; 5. Apis 

 mellifica Z. 5, skg. and po-cltg. (?) (H. M., Kn.) ; 6. Bombus derhamellus K. j (H. M.) ; 

 7. B. hortorum Z. 5 (H. M.) ; 8. B. lapidarius Z. 5, skg. (H. M., Kn.) ; 9. Halictus 

 calceatus Scop. $, vainly skg. (H. M.); 10. Osmia comuta La/r. 5, skg. (H. M.) ; 11. 

 O. rufa Z. 5 and 5, very freq., skg. (H. M., Budd.). D. Lepidoptera. Rhopalocera : 

 12. Rhodocera rhamni Z., skg. (H. M.); 13. Vanessa cardui Z., very freq., skg. 

 (H. M.) ; 14. V. urticae Z., skg. (H. M.). 



Schmiedeknecht noticed the following bees in Thuringia : — i. Bombus jonellus 

 .A". 5; 2. B. pratorum Z. 5 ; 3. Osmia bicolor ScAr. 5; 4. O. uncinata Gerst.; 

 Schenck saw Osmia rufa Z. i, in Nassau ; and Alfken observed 8 bees at Bremen, 



