PART 111. | THE MECHANISMS OF FLOWERS. 157 
their upper surfaces with pollen. The five inner stamens are still 
bent outwards as far as possible, so as to lie upon the petals and 
be out of the way of insects which alight on the flower. Before 
the period of the outer stamens is over, the stigmas separate and 
expand, so that their papillar surfaces which were hidden before 
are now fully exposed in the middle of the flower. 
As the outer stamens wither, the five imner ones rise up to 
surround the style, which lengthens meanwhile, so that its five 
stigmas stand a little way above the circle of pollen-covered 
anthers. 
Honey is secreted, as. in all our Geraniums, by the outer side of 
the base of each outer stamen, and is collected in a slight hollow at 
_ the base of each sepal: it may be reached by means of a proboscis 
at least 7 mm. long, without which the insect must thrust its head 
into the narrow part of the flower. I have seen Rhingia rostrata 
- in great abundance, sucking up the five honey-drops one after 
_ another with its proboscis, which is 11 to 12 mm. long ; it stood 
first on one petal, then on another, and in older flowers its proboscis 
touched first the stigmas and then the ripe anthers, in younger ones 
the ripe anthers only. It effected cross-fertilisation regularly, but 
at times, in drawing out its proboscis, it must also have effected 
self-fertilisation. I have quite as often found this fly busy eating 
| pollen. I have noted, in all, the following visitors :— 
A. Diptera—Syrphide : (1) Rhingia rostrata, L., s. and f.p., ab. B. Cole- 
| optera—(2) Dasytes flavipes, F., sucking and biting the petals. C. Lepid- 
| optera—(3) Pieris napi, L., very ab., s. (Stromberg, May 15, 1868). See also 
No. 590, II. 
Cross-fertilisation is here insured, at first by the early develop- 
ment of the outer stamens, and afterwards by the position of the 
_ mature stigmas above the level of the anthers ; but sclf-fertilisation 
is not absolutely excluded. I have not included this species in 
_ the foregoing series, because I have not yet made sure whether 
 self-fertilisation does result in default of insect-visits. 
Geranium silvaticum, L., is not only widely distributed in 
Low Germany and in Britain, but occurs also in the Alps, where it 
_ extends to far above the limit of trees and is one of the most 
- abundantly visited plants. I have found upon its flowers :— 
| Coleoptera, 8 ; Diptera, 21; Hymenoptera, 24 (Apide, 17) ; Lepid- 
) optera, 21: in all, 74 species. | 
fe This plant is historically interesting, since it suggested to 
_ Sprengel the first idea of his theory. It is also remarkable for 
} being gynodiecious, and for exhibiting transitions both towards 
