66 ANGIOSPERMAE—DICOTYLEDONES 



in a later stage of anthesis, the latter bend out towards the somewhat remote petals, 

 after which the outer set of anthers dehisce, while those of the inner stamens are 

 still unopened. The centrally placed stigma — which is now mature — cannot therefore 

 receive pollen from the same flower, but may be cross-pollinated if insects that 

 have visited other blossoms alight upon it. At a still later stage the anthers of 

 the inner stamens dehisce so that self-pollination may take place if insect-visits have 

 failed. Fritz Miiller states, however, that this is ineffective in South Brazil, though 

 in England — according to Darwin — the contrary is true. It is remarkable that 

 Brazilian plants sent by Fritz Miiller to Charles Darwin were to some extent self- 

 fertile. Hildebrand found the plant to be almost self-sterile in Germany. 



Visitors. — In sunny weather I observed the bright )'ellow flowers to be visited 

 by numerous individuals of a species of hover-fly (Syrphus ribesii Z.), which alighted 

 in an erratic fashion sometimes upon the stigma, sometimes upon the stamens or 

 petals, so that at times they eff'ected cross-pollination, at other times self-pollination. 

 I frequently saw five or six of these flies in a single flower, and they remained there 

 so persistently that I could pluck the flower and examine it with a lens, while the 

 visitors remained undisturbed and continued to devour pollen. They were thickly 

 covered with this on the head, and especially on the upper- and under-surfaces 

 of the thorax. Herm. Miiller observed another hover-fly (Helophilus floreus Z.) 

 visiting the flowers. 



43. Sanguinaria L. 



Pollen flowers devoid of nectar and nectar-guides. 



145. S. canadensis L. (Loew, ' Blutenbiol. Beitrage,' I, pp. 9, 10.) — In this 

 North American plant the inner stamens project a litde beyond the stigma, while 

 the outer ones are somewhat shorter. 



Visitors. — Loew observed in the Berlin Botanic Garden, Apis and Bombus 

 terrester Z. 5, both po-cltg. 



2. Suborder Fumarieae DC. 



Literature. — Hildebrand, Jahrb. wiss. Bot., Leipzig, 1869; Knuth, ' Bl. u. 

 Insekt. a. d. nordfr. Ins.,' p. 23. — The flower mechanism of the species of this family 

 has been thoroughly and carefully investigated by Hildebrand, and Hermann Miiller 

 has determined the visitors. The following remarks are chiefly based upon the 

 researches of these two investigators. 



The Fumarieae bear homogamous bee flowers of peculiar structure. Being 

 as a rule large and brightly coloured, often aggregated into racemes, and not 

 infrequently exhaling a more or less strong odour of honey, these naturally attract 

 insects. The nectar is secreted and concealed in spurs or pouches of the petals, 

 and there are either two such nectaries (Diclytra and Adlumia), or only one (Cory- 

 dalis, Fumaria). The two inner petals are fused at the tip, and so form a hood-like 

 sheath, which encloses anthers and stigmas. This hood is pressed downwards or 

 to the side by nectar-seeking bees, but when the pressure is removed it usually 

 springs back by elasticity to its original position. Bees dust themselves with pollen 

 in the younger flowers, and transfer some of it to the stigmas of older flowers that 



