SY M EETAL.E. The Sympetah• are the ranking phints of the plant kingdom and are also those most recently evolved. While they a number shrubs and trees in the tropics, they are by no means so extensively represented in temperate regions by shrubs and trees as are the •rchichlamydeee. The prominent facts of their distribution are as follows: the earlier groups of angiosperms (Archichlatnydeee and mono cotyledons) were massed in the tropics, the tem perate and boreal regions being relatively poor in true flowering plants. The Sympetalle, there fore, while largely represented in the tropics, found the temperate and boreal regions compara tively free for occupation. and it is in these regions that they have become peculiarly domi nant. This does not mean that there are not more Sympetahe in the tropics than in the tem perate regions, for the proportion of species in favor of the former is about three to two: but it does mean that this is about the normal ratio of tropical increase, which is far exceeded by the other groups. Accordingly. of the Sympe tahe alone can it be said that their distribution throughout tropical and temperate regions is ahout uniform. The families of are not only better defined structurally than those of the Archichlamydere, but their geographical dis tribution is much more definite. This follows the fact that they are more highly specialized and more definitely related to environment than are the Archichlamydea% Among the Sympe take, three families, the plantains. mints, and composites, have a world-wide distribution. The Compositx, as the ranking family of the plant kingdom, and also the youngest and largest, de serves special mention. It includes at least 1°_, O00 species. which, although found everywhere, are most numerous in the temperate regions, where they constitute from one-tenth to one seventh of all of the seed-bearing, plant: of every flora. They are especially characteristic of tem perate America. where asters. goldenrods, sun flowers, etc.. abound. Two great no'-tie temperate families, the figworts and the borages, have also been developed: and the heaths form a family characteristic of boreal conditions.
The impress a peenliar region may have upon the general aspect of its' vegetation, resulting in the assumption of the same general appear a nee by plants of the most relationships, is illustrated by the fact that many families of South Ameriea are eharaeterized by a heath-like habit. the region being known as one of the heath-like plants. There is no smelt notable continental pairing as is shown by the A reli iehla and the monocotyledons. due probably to the fact that extensive forests and boreal distribution permit free intermingling of continental flora. Among tropical Sympetake,
however, the pairing is somewhat evident, and in tropical display America is distinctly domi nant. It is also worthy of note that there is a remarkable paucity of aquatic plants among e'Sympetal.e, as compared with Archiehlainydeee and with monocotyledons. This seems to be re sated to the fact that the two bitter groups had already become well established in fresh and brackish waters, while it wits the temperate and boreal land surface that was especially free for occupation by the Sympetabe.
l'oxerxstos. Through the lapse of time since the advent of plant life upon the earth, the meteorological factors. wind, moisture. heat, and light, have been at work as plant distributors. At divers times and in many part: of the world their work has been interrupted, assisted, or ren dered nugatory by geological agents—glaciers, especially of the ice age, which driven vege tation before them and exiled many plants from their pristine homes; seismic upheavals or sink ings, the former interposing tall mountain ranges, the latter wide oceans. beyond which certain species could not migrate, and which to a greater or less degree isolated these species. sometimes genera, families, and even tribes. The efforts of these factors and agents have been and are assisted by man, by other animals, and by plants: the first either wittingly carrying use ful or ornamental species from country to coun try, or more often unwittingly introducing use less or even noxious ones; the second in a more limited range transporting seed either in or on their bodies: the third breaking down and dis integrating rock. beccming incorporated with the detritus and thus affording a habitation to a succeeding plant. society. Far from having (-eased their labors, these meteorological and geological agents, working in conjunction or in conflict, still profoundly influence the ceaseless change in the distribution of plants.
BIBLIOGRAPHY. Contejean : bataBibliography. Contejean : bata- ?ague (Paris. 18811: Dreide, Handbuch der Pflan:engeographie (Stuttgart, 1890) ; id.. Man uel de gi'ographie botanique Paris, 1897) : De Candolie, ('Wographie hotanique raisonni'e (Paris, 1855) Engler, Versurh timer Enheick lungsaeschichte der ext•at•opisehen Floren gebiete (Leipzig. 1879 ; Engler and Drude. Die Vegetation der Erde 4 vols., Leipzig. Orkebach, Vegetation der Erde (Leipzig, 18841; Sehimper. Pfiantengt ograph oaf physi ologiseher arum-gage (•ena, 189s'l : Wallace, Island Life (New York. 1895) : Warming. Ocko logische Pllan:engeographir (Berlin. 18961. The ecological aspects of distribution are touched upon tinder the following heads: EcoLocv; AL