172 MORPHOLOGY OF THE ANGIOSPERMS 



The majority of angiosperms are pollinized by other groups of insects 

 — ^bees, flies, moths, and butterflies. Nectaries of many forms and varied 

 morphology secrete attractive fluids in positions correlated with the 

 habits and structure of the insects and with the locations and dehiscence 

 types of the stamens. With extrorse anthers, nectaries are usually at the 

 base of the flower outside the stamens; with introrse dehiscence, inside 

 the stamens. (Nectary position is further discussed at the end of this 

 chapter. ) 



In many tropical and some temperate taxa, birds are the chief pol- 

 linizers. It is believed by some students of ornithophily that the extent 

 of this method of pollination is underestimated. Birds have been re- 

 ported as visiting the flowers of more than four hundred genera in many 

 families scattered throughout angiosperms. Visitation of the flowers of 

 a species by birds seeking nectar does not, of course, necessarily mean 

 that pollination occurs in this way, but the evidence to be found in 

 many of these taxa seems unquestioned. Among families in which bird 

 pollination is prominent are the Proteaceae, Gesneriaceae, Nyctagina- 

 ceae, Passifloraceae, Epacridaceae (part), Marcgraviaceae, Violaceae 

 (tropical genera), Leguminosae (woody, tropical genera), Myrtaceae, 

 Bignoniaceae. Some well-known genera reported as pollinated in part 

 by birds are Loronthus, FAicahjptus, Vanilla, Batihinia, Carina, Gladiolus, 

 Fuchsia, Acacia, Xanthorrhoea, Cattleija, Pritcliardia, Cereiis, Anigozan- 

 thus. Aloe, Lonicera, Agave, Miisa, Jacaranda, Callistemon. 



Some unusual features of flower structure have been considered 

 adaptations to bird pollination: the stipitate, compound ovary (not the 

 stipitate follicle, which is primitive) — the ovary borne above the basal 

 nectaries and away from possible injury by the beaks of birds, as in the 

 Proteaceae and Capparidaceae; the ovary protected by sheaths of fused 

 stamens, as in primitive tropical Mai vales. 



Pollination by bats is believed to occur in a few tropical genera, such 

 as Kigelia, Diirio, Freycinctia, Erythrina, Barringtonia. Snails are be- 

 lieved to pollinate some aroids and aquatic plants. 



Pollination by water is obviously an acquired method. It may be by 

 contact of flowers on the surface of the water where the staminate 

 flowers break free and float to the pistillate, as in Elodea and Vallisneria; 

 or by pollen floating submersed, as in Zostera, Halophila, Cymodocea, 

 Najas, and some species of Pofamogefon. (Other aquatic plants have 

 aerial inflorescences, with pollination by wind or insects — many species 

 of Potamogeton.) Perhaps the most remarkable method of pollination is 

 that of Cemtophi/lhim, where distribution of pollen is by both air and 

 water. The stamens, freed from submersed floweis, rise to the surface 

 of the water and there discharge the pollen, which sinks slowly through 

 the water to the pistillate flowers. 



