426 



ANGIOSPERMAE—MONOCOTYLEDONES 



856. Iris Tourn. 



Literature.— Kolreuter, 'Vorlaufige Nachricht,' p. 21 ; Sprengel, 'Entd. Geh.,' 

 pp. 69-78. 



Herkogamous humble-bee or hover-fly flowers with large, arched, petaloid 

 stylar branches. 



2677. I. Pseudacorus L. (Sprengel, loc.cit.; Herm. JluUer, 'Fertlsn.,' p. 543; 

 MacLeod, Bot. Jaarb. Dodonaea, Ghent, v. 1893, pp. 315-16; Ludwig, Biol. 

 Centralbl, Erlangen, vi, 1887 ; Kirchner, ^ 



' Flora V. Stuttgart,' p. 80; Knutli, ' Bloemen- 

 biol. Bijdragen.')— The large, yellow, odourless 

 flowers of this species possess a nectar-guide 

 on the sepals in the form of a dark-yellow 

 patch bordered by a brown, zig-zag line ; lines 

 of the same colour also lead to the inside of 



Fig. jyi. Irii Picudacorus,, L. (1-3. after Hcrm. Muller, 4. from nature). (i) Transverse section 

 through the perianth tube. 12) Do., through the perianth, at the point where the sepals and petals become 

 free. (3) Transverse section somewhat higher than (2), showing the boundaries of the nectar-passages, 

 a, style; a' a' a', petaloid stylar branches ; ^, nectar-passages; c, adherent part of filament; ddd^ sepals; 

 rf'rf'rf', petals; ece, ridges on sepals. (4) Flower from the side (X 2): one of the three petaloid stylar 



branches is lifted up to show an anther (a) and a stigma (i) ; p, sepal with nectar.guide ; /, petal. 



the flower, where nectar is secreted by the base of the perianth, and stored in the tube 

 between this and the style. The only means of access is found between the three large 

 sepals, which serve as platforms, and the three petaloid stylar branches situated above 

 them. Each of these three entrances is divided into two separate tubes by the fila- 

 ments, which are fused with the sepals. Visitors seeking nectar creep forward on the 

 platform under the stylar branch, bending back the upper side of the litde stigmatic 

 lappet in doing so, and dusting it with the pollen brought from another flower. In 

 creeping further, the insect brushes against the anthers, which have dehisced down- 

 wards by two longitudinal slits, and dusts its back with fresh pollen. After having 

 extracted nectar it creeps out backwards, but is unable to brush against the upper 

 side of the stigmatic lobe again, as it has once more sprung upwards. Cross-pollina- 

 tion therefore takes place regularly, and occasionally also self-pollination as an 

 exception ; the latter, however, cannot occur automatically. A proboscis 7 mm. long 

 is necessary to reach the nectar, and 15 mm. long to suck it all out. 



The flowers occur in three oecological forms : — 



(a) bomhophila Knuth. The stylar branches are situated 6-10 mm. above the 

 corresponding sepals. This distance corresponds to the height of a creeping humble- 



