62 ANGIOSPERMAE—DICOTYLEDONES 



anthers of the three lowest stamens, so that automatic self-poUination regularly takes 

 place, and this is largely made use of by the plant, for scarcely any insect visitors 

 have so far been observed. 



Kerner states that each flower opens and closes three times, after which it does 

 not open again. During the periodic closing of the corolla, the pollen which cHngs 

 to it is brought into contact with the stigma and autogamy consequently eff'ected. 

 During unfavourable weather the flowers remain closed and self-pollination takes 

 place pseudo-cleistoganiously. {C/. Fig. 236.) 



It is possible that the delicate clavate hairs covering the filaments may be used 

 by visitors as food, in addition to the pollen. 



Visitors. — Smith (England) saw the bee Halictus morio F. 



1800. A. caerulea Lam. ( = A. arvensis Z., according to the Index Kncensis). 

 (Herm. Muller, loc. cil.) — The flower mechanism of this species is exactly the same 

 as that of A. arvensis. It must, however, be regarded as a distinct species, for Clos 

 states that when crossed with the latter no seeds capable of germination are produced. 



1801. A. tenella L. — The plants of this species observed by iMacLeod on the 

 dunes of Flanders bore white or reddish pollen flowei's, with red-violet longitudinal 

 streaks on the corolla-lobes. The corolla-tube is deeper than in the two last species, 

 and is quite filled up by the hairs covering the filaments. The sligma projects 

 2-3 mm. beyond the anthers, so that automatic self-pollination cannot take place. 



541. Centunculus Dill. 

 Inconspicuous homoganious pollen flowers. 



1802. C. minimus L. (Ascherson, Bot. Zig., Leipzig, .xxix, 1871, p. 553: 

 Herm. .Miiller, 'Fertilisation,' p. 390; Kirchner, 'Flora v. Stuttgart,' p. 535; 

 Kerner, ' Nat. Hist. PI.,' Eng. Ed. i, II, pp. 170, 213, 332 ; Knuth, ' Bl. u. Insekt. a. 

 d. nordfr. Ins.,' p. 121, ' W'eit. Beob. ii. Bl. u. Insekt. a. d. nordfr. Ins.,' p. 230.) — 

 In this species the very small white or reddish flowers are regularly self-pollinated, 

 for in unfavourable weather they remain closed and pseudo-cleistogamy obtains. 

 Crossing is now and then possible, however, for Kerner says that the flowers open 

 for a short time in bright sunshine between 10 and 11 a. m. 



In the island of Fohr I noticed numerous purely cleistogamous flowers. 



542. Androsace L. 



Literature. — Herm. j\Iiiller, ■ Alpenblumen,' pp. 357-8. 



Homogamous (also protogynous according to Kerner) flowers, with concealed 

 nectar secreted in favourable weather only by the surface of the ovary and hidden in 

 the shallow (i|-2 mm.) corolla-tube. This narrows above, leaving only a very small 

 aperture, so that although the nectar is not deeply concealed, it can only be found by 

 the more intelligent insects, an orange-coloured nectar-guide indicating its position. 

 When Lepidoptera, bees, or the more skilful flies insert their proboscis into the 

 narrow opening of the flower, one side of this touches the stigma and the other side 

 the anthers, so that crossing is ensured. Should insect-visits fail, self-pollination is 

 secured by the nearness of the anthers to the stigma in the liomogamous flowers. 



