194 THE FERTILISATION OF FLOWERS. [PART III. 
bend over its papillar surface, protecting it from immediate con- 
tact with the insect-visitor. Gradually these hairs wither, so that 
in older flowers the stigmatic papillz are freely exposed (5, Fig. 64), 
and at the same time the style bends more and more inwards, so 
that the stigma protrudes farther and farther from the carina. 
_Cross-fertilisation is thus insured and self-fertilisation prevented 
in case of insect-visits, while spontaneous self-fertilisation is also 
prevented in absence of insects. 
The most remarkable peculiarity in the flowers of the La- 
burnum is that, like those of Orchis mascula, O. morio, &c., they 
only supply nectar inclosed in cellular tissue. The ordinary . 
secretion of honey and the ordinary means of access to the honey — 
Fic. 64.—Cytisus Laburnum, L. 
1,—Basal part of an old flower, seen from above, after removal of calyx and vexillum. 
2, 8, 4.Stigmas of younger flowers. 
5.—Stigma of an old flower. 
aa, cut base of calyx; b, point of insertion of vexillum ; ¢, fleshy eminence, anterior to insertion — 
of vexillum, which is probably probed by insects ; d, claw of ala; e, shallow pouched depression of 
saps which fits into a corresponding depression on the upper surface of the carina; f, carina; 
g, its cleft. 
are here wanting, and the stamens are monadelphous; but in~ 
front of the point of attachment of the vexillum is a thick, fleshy 
swelling, so rich in honey that if a fine glass tube be inserted in it 
a column of clear fluid ascends the tube. The vexillum is marked 
with dark lines pointing towards the base of the flower, which can 
only be interpreted as pathfinders, and an insect’s proboscis inserted 
beneath the vexillum comes without fail to the nectary. I have 
seen both bees and butterflies inserting their tongues into numerous - 
flowers in succession, spending some time on each; the bees had 
their pollen-baskets empty, and were therefore not engaged in 
collecting pollen, It seems therefore impossible to doubt that the 
swelling at the base of the vexillum is actually pierced by bees 
and butterflies for the sake of its secretion. ; 
