VIOLARIEAE 135 



place by the fall of pollen. This kind of pollination is inevitable when the flowers 

 close at night, or in dull weather. 



Visitors. — In Capri I noticed that a beetle— Oxythyrea squalida Scop. — was 

 the almost exclusive visitor and pollinator, the pollen readily adhering to its hairy 

 body. Less frequently a bee of medium size — Halictus sp. — made its appearance 

 and collected pollen on the tibiae of its hind-legs. Both insects usually first alighted 

 on the stigma, and therefore effected cross-pollination. 



Schletterer observed the following at Pola. — 



Hymenoptera. (a) Apidae: i. Andrena cyanescens Nyl.; 2. A. dubitata 

 Schenck ; 3. A. nana K.\ 4. A. parvula K. ; 5. Halictus interruptus Pz. {d) Pompilidae : 

 6. Pompilus rufipes Z. (c) Tenthredinidae : 7. Amasis laeta /'. 



XIII. ORDER VIOLARIEAE DC. 

 The most important genus of this order is — 



112. Viola Tourn. 



The species of this genus mostly possess large brightly-coloured flowers, in 

 which yellow, violet, and blue predominate. The anterior (lower) petal is spurred, 

 giving the flowers their characteristic form, from which alone we might infer that 

 they were adapted to particular groups of insects. Most species of violets and the 

 like are bee flowers, Diptera and Lepidoptera playing a comparatively unimportant 

 part as pollinators. In certain species, however — e. g. V. calcarata — the spur is so 

 long that only the proboscis of Lepidoptera can reach the nectar. There are, on the 

 other hand, violets with so short a spur — e.g., V. biflora — that they must be described 

 as fly flowers. The species of Viola therefore chiefly belong to the flower class Hb, 

 but some of them are included in the classes L and F. All are homogamous. 



The anther of each of the two lower stamens possesses — as Sprengel long ago 

 admirably described — a nectar-secreting process, which projects into the spur of the 

 corolla where the secretion is stored. The connective of each of the five stamens 

 is produced into a membranous appendage. As these appendages overlap one 

 another laterally and also clasp the style underneath the stigma, they form 

 a conical chamber, into which the dry pollen falls when the anthers dehisce. 

 The stigma projects beyond this cone, and closes the entrance to the flower, so that 

 an insect probing for nectar must first touch it, and then raise it up so as to open 

 the anther cone, from which pollen falls on to the upper surface of its proboscis. 

 And since visitors are in the habit of thrusting the proboscis only once into each 

 flower, they must regularly effect cross-pollination. In many species cleistogamous 

 flowers with vestigial corollas have been observed, as well as the ordinary open ones. 

 (Cf. Vol. I, pp. 51, 58-) 



342. V. odorata L. (Sprengel, ' Entd. Geh.', p. 394 ; Herm. MuUer, ' Fertilisa- 

 tion,' p. 119, ' Weit. Beob.,' II, p. 209; Hildebrand, 'Die Geschlechtsvert. b. d. Pfl.'; 

 Kerner, 'Nat. Hist. PI.,' Eng. Ed. i, II, p. 200; Schulz, 'Beitrage,' II, p. 205; 

 MacLeod, Bot. Jaarb. Dodonaea, Ghent, vi, 1894, pp. 221-2, Arch, biol., Paris- 

 Bruxelles, vii, 1886 ; Knuth, ' Bloemenbiol. Bijdragen ' ; Kirchner, ' Flora v. Stuttgart,' 

 p. 318; Warnstorf, Verb. bot. Ver., Berlin, xxxviii, 1896.) — The inconspicuousness 



