226 ANGIOSPERMAEDICOTYLEDONES 



branches are still unreceptive, the flower is purely male at this stage. But, even 

 before all the five outer anthers have dehisced, these branches begin to diverge. 

 The outer stamens next bend towards the middle of the flower, and their anthers 

 dehisce. In the final stage, the anthers stand between and somewhat above the 

 stigmas, so that insect visitors may effect either cross- or self-pollination. In the 

 absence of such visitors, automatic self-pollination necessarily occurs. 



Warnstorf describes the flowers as homogamous and autogamous, and states 

 that the pollen-grains are yellowish, spherical, covered with reticulately arranged 

 tubercles, and about 63 /x in diameter. 



At Blankenberge, besides the protandrous hermaphrodite flowers, MacLeod 

 observed female ones with anthers devoid of pollen, and also intermediate forms, 

 in which only some of the stamens were sterile. 



Visitors. Hermann Miiller observed the following. 



A. Diptera. (a) Conoptdae: 1. Dalmannia punctata F., skg. ; 2. Myopa 

 testacea Z., do. (b) Muscidae: 3. Scatophaga merdaria F., skg. (c) Syrphidae: 

 4. Ascia podagrica F, very freq., skg. ; 5. Helophilus pendulus Z., skg. ; 6. Rhingia 

 rostrata Z., do.; 7. Syritta pipiens Z., do. B. Hymenoptera. (a) Apidae: 8. 

 Andrena gwynana K. 5, skg. ; 9. Apis mellifica Z. 5, do. ; 10. Chelostoma campanu- 

 larum K. 5, do. (Buddeberg); 11. Halictus nitidus Schenck j, do. ; 12. H. sp., do. 



On June 5, 1897, I saw the following in Helgoland. 1. Eucera difficilis (Duf.) 

 Per. S, skg.; 2. Lucilia caesar Z., do.; 3. Syritta pipiens Z., hovering for some time 

 before the flower, then skg. and po-dvg. ; 4. Andrena labialis K. t, skg. 



H. de Vries in the Netherlands (Ned. Kruidk. Arch., 2. ser., 2. deel, Nijmegen, 

 1875) noticed a humble-bee, Bombus terrester Z. 5; and MacLeod observed 6 bees, 

 4 hover-flies, 2 Muscidae, and a Lepidopterid (Bot. Jaarb. 

 Dodonaea, Ghent, vi, 1894, pp. 232-3). 



Loew (' Beitrage,' p. 60) saw the bee Melithreptus 

 menthastri Z. in Switzerland; while at Pola Schletterer 

 observed a saw-fly, Cladius pectinicornis Fourcr., and the 

 following bees: 1. Andrena dubitata Schenck; 2. A. fla- 

 vipes Pz. ; 3. A. parvula K.; 4. Halictus calceatus Scop. ; 

 fig. 69. Geraniumjusii- c. Osmia versicolor Ltr. 



lum, L. (after Herm. Mailer). 



stamens and pistil of a just In Dumfriesshire, a short-tongued bee, a hover-fly, 



stigmas. Wer "' a " ers ' -f ' and several Muscidae have been recorded (Scott-Elliot, 



' Flora of Dumfriesshire/ p. 39). 



571. G. pusillum L. (Herm. Miiller, Fertilisation,' pp. 154-5, 'Weit. Beob.,' 

 II, p. 217 ; Kirchner, ' Flora v. Stuttgart,' p. 339 ; Knuth, ' Bl. u. Insekt. a. d. nordfr. 

 Ins.,' pp. 50-1.) As Hermann Miiller explains, the small lilac flowers of this plant 

 are even less conspicuous than those of the last species, so that insect visitors 

 are still less numerous, and automatic self-pollination constantly takes place before 

 the end of anthesis. Although the flowers of the two species are externally very 

 similar, their mechanisms are quite different. G. pusillum is protogynous, with 

 persistent stigmas. Only the five inner stamens those with nectaries at their 

 bases bear anthers. When the flower opens, the stigmatic branches have ahead)' 

 half spread out, while the anthers lying between them are still immature. On 

 dehiscence of the latter, the stigmatic branches diverge still more, and the stamens 



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