556 BOTANY PART n 



surface of the insect's body (Fig. 528, 1, 3). On visiting an older 

 flower the insect will meet with the stigma projecting further from the 

 upper lip on the elongated style (Fig. 528, 2). The stigma is then in the 

 position corresponding to the depressed half-anthers, and will receive 

 with certainty the pollen deposited from them on the back of the bee. 



In addition to the stimulus of hunger, plants utilise the reproductive instinct 

 of insects for securing their pollination. Not a few plants (Stapetta, Aristolochia, 

 and members of the Araccae), by the unnatural colour of their flowers combined 

 with a strong carrion-like stench, induce carrion-flies to visit them and deposit 

 their eggs ; in so doing they effect, at the same time, the pollination of the flowers. 

 In the well-known hollow, pear-shaped inflorescences of the Fig (Ficus carica, 

 Fig. 614) there occur, in addition to long-styled female flowers that produce seeds, 

 similar gall-flowers with short styles. In each of the latter a single egg is laid by 

 the Gall- wasp (Blastophaga], which, while doing this, pollinates the fertile flowers 

 with pollen carried from the male inflorescence (the Caprificus). The large white 



* 2 



FIG. 528. Pollination of Salvia pratensis. Explanation in the text. (After F. NOLL.) 



flowers of Yucca are exclusively pollinated by the Yucca moth (Pronula). The 

 moth escapes from the pupa in the soil at the time of flowering of Yucca and 

 introduces its eggs into the ovary by way of the style ; in doing this it carries 

 pollen to the stigma. The larvae of the moth consume a proportion of the ovules 

 in the ovary, but without the agency of the moth no seeds will be developed, as 

 is shown by the sterility of the plant in cultivation. 



ORNITHOPHILY plays a much less important part than entomophily ; the bird- 

 visitors are confined to the American Humming-birds and the Honey Birds of the 

 Old World. A specially remarkable case of adaptation of this kind is afforded by 

 Strelitzia reginae, which is often cultivated in greenhouses (Fig. 529). Its three 

 outer perianth segments (t) are of a bright orange colour ; the large azure-blue 

 labellurn (p) corresponds to one of the inner perianth leaves, while the other two (p) 

 remain inconspicuous and roof over the passage leading to the nectary. The 

 stamens (st) and the style (</) lie in a groove, the margins of which readily 

 separate, formed by the labellum, while the stigma (q) projects freely. The similarly- 

 coloured and showy bird (Nectarinia afro) flies first to the stigma and touches it, 

 then secures pollen from the stamens, which it will deposit on the stigma of the 

 flower next visited. 



The structure of the pendulous inflorescence of Marcgrama is just as remarkable 

 (Fig. 530) ; in this the bracts form receptacles containing the nectar. Numerous 

 insects fly around these nectaries, and the darting Humming-birds, either in pursuit 



