pPART ut| = THE MECHANISMS OF FLOWERS. 245 
usually larger and more conspicuous than the female, so in the 
Y three distinctly proterogynous species of Saxifraga, the: flowers 
while in their male stage are more than twice as large as they were 
at first while in their female stage. As Sprengel “supposed, it is 
i; probable that many insects are thus induced to visit the male 
flowers first, and then, having dusted themselves with pollen, to 
proceed to the female flowers and fertilise them. The annexed 
- figure may serve to show this distinction between the flowers in 
their male and female stages. 
The honey is quite visible in the above-named species of 
| Sawifraga, except S. oppositifolia. Very various short-lipped 
insects, but especially flies, serve therefore as fertilising agents. 
To the selective influence of flies, therefore, the development of 
_ the ordinary colours—white, dull-yellow, white with yellow or purple 
spots—must be mainly ascribed. In particular, the prettily dotted 
petals of S. rotundifolia and S. umbrosa, L., seem to be due to the 
nfluence of certain elegant and prettily coloured Syrphide by which 
they are especially visited and cross-fertilised (S. rotundifolia by 
— Sphegina clunipes and Pelecocera sccevoides; S. umbrosa by Ascia 
podagrica). 
| _— Saxifraga aizoides, L., with its large golden flowers dotted with 
_ orange, is the most conspicuous form, and attracts most insect-visitors. 
I have found it to be visited by 126 species of insects (Coleoptera, 
; Diptera, 85; Hymenoptera, 20; Lepidoptera, 13). (609.) 
The honey is most deeply placed in S. oppositifolia ; the flowers 
_of this species are diligently and persistently visited by butter- 
flies and are arrayed in carmine or purple, the favourite colour 
_ of most of these insects.! 
5 
h 
q 
5 
3 
; 
155. CHRYSOSPLENIUM ALTERNIFOLIUM, L.—The flowers have 
a great superficial likeness to the apical flowers of -Adoza, and 
are visited by a very similar set of tiny insects. 
From the middle of the flower the two styles stretch, diverging 
and bending outwards slightly, capped at the apex by the smooth, 
capitate stigmas, and surrounded at the base by a broad, fleshy, 
yellowish disk, secreting numerous minute drops of honey. At 
_ the edge of this disk the calyx, which coalesces below with the 
_ ovary, expands horizontally into four broad rounded sepals, bright 
_ yellow, and slightly recurved. There is no trace of petals. Be- 
_ tween each pair of sepals, and also facing each one, there stands on 
the edge of the disk a stamen, erect, and reaching as high as the 
1 609, Figs. 26-38 ; in connection with S. wmbrosa, see 604. 
