Age and area; a study in geographical distribution and origin of species . eylon endemicgenus of Dipterocarpacese, has 11 species, whose local distribu-tion (fig. on p. 153) is typical of that of many local genera, orgenera with many species (mostly endemic) in one whole range of the genus (about 4000 square miles in south- ch. xv] ENDEMISM AND DISTRIBUTION: SPECIES 153 west Ceylon) is occupied by one of its species, D. zeylanica, whilethe others occupy smaller and smaller areas within this, downto a comparatively few square miles. This is perhaps the mostcommon type of distributi
Age and area; a study in geographical distribution and origin of species . eylon endemicgenus of Dipterocarpacese, has 11 species, whose local distribu-tion (fig. on p. 153) is typical of that of many local genera, orgenera with many species (mostly endemic) in one whole range of the genus (about 4000 square miles in south- ch. xv] ENDEMISM AND DISTRIBUTION: SPECIES 153 west Ceylon) is occupied by one of its species, D. zeylanica, whilethe others occupy smaller and smaller areas within this, downto a comparatively few square miles. This is perhaps the mostcommon type of distribution with genera of small area, whichupon the theory of Age and Area are to be regarded as youngbeginners. Another instance is Haastia in New Zealand (fig. onp. 154). Distribution of the same type, but more extended, is shownby the (chiefly endemic) species of Ranunculus1 in New Zealand(fig. on p. 156), and by very many other genera in that coun-try. In this map the widely distributed species, those occur-ring outside of New Zealand, are shown by dotted lines, and it. will be noticed that three of them range all over New Zealand(including the little Stewart Island to the south), and also to theChathams, 375 miles to the eastward, while the fourth onlyranges from the far south up to the middle of North Island. Theendemics all have ranges within that of the first three wides,among which probably, upon the general implications of Ageand Area, one must principally look for their parent or endemic with the greatest range covers slightly more groundthan the wide of least range, and the others occupy smaller andsmaller areas, becoming steadily more numerous in going south,till a maximum is reached a little south of the middle of SouthIsland, as indicated in the following figures (cf. p. 77), which 154 ENDEMISM AND DISTRIBUTION: SPECIES [pt. n J ,. » — 1 HA/ * ySTIA Diagram showing the areas occupied by the species of Haastia inNew Zealand.(By courtesy of the Editor,
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