390 ANGIOSPERMAE—DICOTYLEDONES 



When the homogamous flowers open the anthers of the outer stamens dehisce, 

 while those of the inner ones remain for some time beneath the receptive stigmas. 

 As most of the visitors settle in the middle of the flower, and therefore touch 

 the stigmas first, they regularly effect crossing. Only the honey-bee usually pushes 

 in between the petals and stamens to reach the nectar, and so may effect self- 

 pollination as well. Failing insect-visits, Stadler says that automatic self-pollination 

 is possible, while Focke and Waite state that the species is undoubtedly self-fertile. 

 Large fruits often contain only empty pips. 



Focke describes the species as andromonoecious. When hermaphrodite flowers 

 are dusted with pollen taken from the male flowers of the same plant they are 

 almost always sterile, though they are fertile with pollen taken from another plant. 



Visitors. — Herm. Miiller observed the following. — 



A. Coleoptera. Coccindlidae: i. Rhizobius litura Z'., creeping about in the 

 flowers. B. Diptera. Muscidae: 2. Lucilia cornicina F. C. Hymenoptera. 

 Apidae : 3. Andrena albicans Mull. 5, vainly searching for nectar, and then po-dvg. ; 

 4. A. fulva Schr. }, po-cltg. ; 5. A. gwynana K. $, do. ; 6. Anthophora pilipes F. S 

 and $, skg. ; 7. Apis mellifica L. 5, generally skg., now and then also po-cltg.; 

 8. Bombus muscorum F. j, skg. ; 9. B. pratorum 5 and 5, persistently skg. ; 10. B. 

 rajellus K. $, skg.; 11. B. terrester L. 5, persistently skg. ; 12. Halictus rubicundus 

 Chr. 5, po-cltg. 



Alfken noticed the following bees at Bremen : — i. Bombus agrorum F. 5 ; 2. B. 

 derhamellus K.<^; 3. B. lucorum L. J and 5 ; 4. Halictus calceatus Scop. $. 



Schletterer, at Pola, saw the southern humble-bee Bombus argillaceus Scop., 

 flying about the flowers on quiet sunny days in [January. 



931. C. vulgaris Pers. ( = Pyrus Cydonia Z.). (Dodel-Port, 'Biol. Atlas d. 

 Botanik'; Kirchner, 'Flora v. Stuttgart,' p. 428.) — The large reddish-white flowers 

 of this species are protogynous. The nectar is protected against small unbidden 

 guests by hairs on the style, and by the incurved bases of the filaments. Small 

 creeping insects are kept out by the recurved sepals, which are covered with 

 glandular hairs below, and also by the thick hairs on the bases of the petals. 

 In other respects the mechanism agrees with that of Crataegus Oxyacantha. 

 Automatic self-pollination is not excluded. 



Visitors. — Loew observed a bee (Halictus nitidiusculus K. 5), po-cltg., in the 

 Berlin Botanic Garden. 



266. Pyrus L. 



White or red protogynous flowers of considerable size ; with half concealed 

 nectar secreted by the receptacle. 



932. P. Malus L. (Hildebrand, 'D. Geschlechts-Vert. b. d. Pfl.,' p. 60 ; Herm. 

 Miiller, ' Fertihsation,' p. 238; Kirchner, ' Beitrage,' pp. 36-8; Waite, ' Pollination 

 of Pomaceous Fruits.') — Hildebrand was the first to figure the projecting position 

 of the stigmas owing to which cross-pollination is favoured, and Hermann Miiller 

 first noticed protogyny in this species. To Kirchner we are indebted for the most 

 exhaustive study of the flower mechanism. The size of the widely expanded reddish- 

 white or rose-coloured blossoms varies with the variety ; in small-flowered ones 

 the average diameter is 38 mm., in large-flowered ones 49 mm. During the day 



