CROSS-FERTILIZATION. 613 CROSS-FERTILIZATION. many visitors. Briglit-roil llnwors attract liul- fertlies; blue flowers are especially attractive to IxH'S, while (lull-yellow or brownish llowers at- tract flies. It has been thought by Darwin, Wallace, T.iib bock, and other-, that the niarkin^'^ of llowers. PURPLE LOOSESTRIFE. Diagrams of t.hre»^ forms of tfowers sfiowiiif^ modiflca- tioDS of relative leii^h cif pistils and stauieiis in adapta- tion to requirements of cross-fertilization: .4, long-styled form; B, mid-styled form; C, short^st.vled. (.fter Wal- lace.) such as lines or spots converging to the centre or nectar, serve as guides to insects; but this is not necessarily the case, since salvia, wistaria, clover, and other flowers which are each of some one color attract bees equally well. H. Miiller has observed that the gentians of the lowlands are visited chiefly by bees, while those of the high Alps are adapted only to butterflies. Most species of Rhinanthus. to which the 'yellow rat- tle' of Europe belongs, are what Wallace calls 'bee-flowers.' but one species confined to the high Alps of Switzerland has been ada])ted to be fertilized by butterflies only. It is now known that flowers did not apjjear until the Jlesozoic age ; they are not known to have existed in the Carboniferous period. Composite flowers, allied to the sunflowers, have been discovered in the Cretaceous clays of Xew .Tersey. and it is prob- able that our large and irregular flowers possibly date back to the Cretaceous period. Tliis was the time when insects that visit flowers also originated. Xo pollen-eating beetles, no moths, butterflies, wasps, or bees are known to have existed in the Carboniferous, nor before the middle or end of the Jlesozoic ; it seems prob- able, therefore, that flowers and the insects which visit them appeared at about the same epoch. We may correlate with this view the theory' of Henslow that the irregular flowers, such as those of the pea. bean, etc., are due to the inter- mittent mechanical stimulus resulting from the visits of butterflies, moths, and bees. He de- pends on the Lamarckian factors of use and disuse, and use-inheritance, to account for the beautifully irregular forms of the papilionaceous and labiate flowers, as well as the singular and gorgeous flowers of the orchids, dispensing with the theory of natural selection. However this may be, in the beginning flowers were most probably small, regular in shape, inconspicuous, and ^If-fertilized. Henslow, and also Wallace, take the view that many inconspicuous and im- perfect flowers, including those that are ^^ind- fertilized, such as plantains, nettles, sedges, and gra.s.ses, do not represent primitive or undevel- oped forms, but have, through the neglect of in- sects, become degenerate types, derived from more perfect forms which were originally adapt- ed to insect fertilization, I'crlilizution of Flowers by Hiidn. — While in the north temperate zone insects a])pear to be the chief means of cross-fertilization of flowers, where this is not caused by the wind, in the tropics an<l Southern Hemisphere, Wallace tells us, birds have iti many cases led to modilications in the form and colors of llowers. Humming- birds are active in performing this office, fertiliz- ing many such blossoms as the passion-flowers, trumpet-flowers, fuchsias, and lobelias. The Salvia splendens of Mexico is especially adapted to their visits: and in the Andes and in ('liile, where these birds are extremely abundant, many kinils of red tubular llowers, often of great size, are apparently adapted to Ihe long, slender bills of these hummers. The most extraordinary
- ulaptatioii to bird-fertilization are the flowers
of Maicgravia, in which, says Wallace, the pedi- cels and bracts of the terminal portion of a pendent bunch of flowers have been modified into pitchers which secrete nectar and attract in- sects, while birds feeding on the nectar or in- sects have the pollen of the overhanging flowers dusted on their bai'ks. and carrying it to other flowers, thus cross-fertilizing them. In the east- ern tropics the sunbirds take the place of the hummers, and they are aided by the flower- peckers. (See DiCyEUM.) In the Australian region there are two flower-feeding groups — the honey-suckers (Meliphagidie) and the brush- tongued lories (Trichoglossida?) . In Xew Zealand the use of animal life in fer- CROSS-FKRTILIZATION BY BIRDS. A humming-bird {Lophornis orn&tus) feeding upon a flower of Marcgravia nepeathofdes, and tn.kingand leavlne pollen by brushing against the overhanging anthers and pistile. tilizing flowers is seen in the ca.se of a country which is remarkably poor in siwcies of insects, especially bees and butterflies; yet it has been shown by local botanists that no less than one- fourth of all the flowering plants of those islands are incapable of fertilization, and thus wholly
