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PART IIT. | THE MECHANISMS OF FLOWERS. 221 
Orv. ROSACEA. 
9 
Tribe Prunee. 
127. PruNUS comMuNIS, Hups., a, (P. spinosa, L.), Blackthorn, 
Sloe.—When the flower opens the style stands some millimetres 
above the stamens, whose anthers are still closed, and which are 
bent down towards the centre of the flower. The stigma is already 
mature, and projects even from the half-open flower; insects, in 
_alighting, come first in contact with it. In due course the petals 
spread out into a plane, and even further; the stamens become 
erect and incline outwards; the anthers dehisce, beginning with the 
outermost; the style also elongates, and overtops the shorter 
stamens immediately around it: its stigma is still fresh, and insect- 
visitors may therefore now lead to self-fertilisation. The flowers 
turn towards the sun, and in default of insect-visits self-fertilisation 
_ may take place by pollen falling on the stigma. 
The numerous white flowers are very conspicuous on the black, 
still leafless twigs ; their abundant honey attracts numerous insects, 
particularly flies and Andrene, all the more that the plant flowers 
early (April and beginning of May) in advance of most competitors. 
ae 
Visitors: A. Hymenoptera—(a) Apidae: (1) Halictus cylindricus, F. 9, s. 
and ¢.p., ab. ; (2) H. albipes, F. 9, ditto ; (3) Andrena dorsata, K. 9, ep. ; 
(4) A. parvula, K. ?,s.ande.p.; (5) A. fasciata, Wesm. ¢, s. ; (6) A. albicans, 
‘K. 2 $, cp. and s.; (7) A. fulva, Schrank, 9,8. and c.p. ; (8) A.:fulvicrus, — 
K. 2 g,s8.; (9) A. Gwynana, K. ?,s. and ep.; (10) A. rose, Pz. 9, s. and 
¢@.p.; (11) A. Schrankella, Nyl. 9, cp. ; (12) A. atriceps, K. 9 ¢, 8.; (13) 
~ Nomada succincta, Pz. ¢,s.; (14) Osmia rufa, L. ¢,s.; (15) Apis mellifica, 
iL. §, s. and ep.; (b) Tenthredinide: (16) Dolerus gonager, Kl. 5. B. 
Diptera—(a) she sa : (17) Empis rustica, Fall, s.; (6) Syrphide: (18) 
‘Eristalis arbustorum, L. ; (19) E. nemorum, L. ; (20) E. intricarius, L., all 
_ three s. and c.p.; (c) Muscide: (21) Scatophaga stercoraria, L.; (22) S. 
| merdaria, F., both sucking; (23) Chlorops, s.; (24) Sepsis, s. ab. ; (25) 
Species of thease: s.; (d) Bibionide: (26) Bibio Marci, L., lh. OC. 
Coleoptera—Nitidulide : (27) Meligethes, Lh. D. Lepidoptera—Rhopalocera : 
8) Vanessa To, L., s. 
‘128. Prunus Papus, L., Bird Cherry—This species agrees on 
__ the whole in its proterogynous arrangement with P. spinosa, but 
ia the stamens remain throughout aired inwards, so that in the 
_ second stage insect visits may lead to self-fertilisation more readily 
_ than in the preceding species. In absence of insects, spontaneous 
 self-fertilisation takes place regularly—since the inner stamens 
