142 



ANGIOSPERMAE DICOTYLEDON ES 



This head, however, rests on a hair-fringed groove in the lower petal, into which the 

 pollen falls either of itself or owing to the pressure of the insect. The proboscis as 

 it passes along the groove gets dusted with pollen on its under-side. The three 

 following varieties may be distinguished. 



(a) V. vulgaris Koch. This variety possesses large flowers, 20-30 mm. long and 

 14-16 mm. broad. The petals are longer than the calyx, and are either all violet, 

 or the four upper ones are violet, while the lower one is yellow with violet veins; or 

 else the lateral petals may also be yellowish. This variety can only be fertilized by 

 cross-pollination. The opening of the spheroidal stigmatic head is turned outwards, 

 so that the pollen, when it escapes from the anther-cone, cannot of itself fall into the 

 stigmatic cavity. On the lower edge of the stigma there is a flexible lip-like valve, 

 which prevents the proboscis of an insect as it is being withdrawn from effecting 

 self-pollination. When on the other hand the proboscis is introduced, it may 

 dust the upper-side of the valve with pollen from another flower, thus bringing about 



Fig. 40. Viola arenaria, DC (after Herm. Muller). A and B, as in Fig. 39. C. Reproductive 



organs, seen from below. D and E. Pistil seen from below and from the side. (A and B X 2$; 



CE X 7.) 



cross-pollination. After the flower has been open a few days the pollen falls of itself 

 out of the anther-cone into the hairy groove of the lower petal. If insect visitors are 

 kept away, the flowers do not wither for two or three weeks, and either no fruits are 

 set, or only a few with seeds incapable of germinating. 



Visitors. I have seen Anthophora pilipes F., and Bombus hortorum Z., both 

 skg., in this large-flowered variety. Hermann Muller observed only long-tongued 

 bees : Apis, Bombus lapidarius, B. terrester, B. hortorum, and Anthophora pilipes F. 

 5 ; all skg. The last-named bee was also noticed by Delpino. 



As further visitors Herm. Muller observed a small bee Andrena albicans Mull. 

 J with a proboscis 2-2^ mm. long. Self-pollination was effected during its fruitless 

 attempts to reach the nectar, which was concealed at a depth of 3 mm. He also 

 observed a hover-fly Syritta pipiens Z. po-dvg., which frequently touched the 

 stigma, and must therefore have effected self-pollination. 



On one occasion Alfken noticed a humble-bee Bombus hortorum Z. skg., 

 in Juist. 



