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Show 464 SUMMARY OF THE OONTENTS. Colossal size and great age of some kinds of treesj Dragon tree of Orotava thirteen, and Adansonia digitata (Baobab) thirty-two English feet in diameter. Characters cut in the bark of the trees in the 15th century. Adanson assigns to some of the Baobab trunks in Senegambia an age of between 5100 and 6000 years . . 283-288 Judging by the annular rings, there are yew-trees (Taxus baccata) from 2600 to 3000 years old. Is it true that, in the northern temperate zone, the part of the tree turned towards the north has narrower annular rings, as Michel Montaigne affirmed in 15811 Species of trees in which individuals attain a size of above twenty-one or twentytwo English feet diameter, and an age of several centuries, belong to the most different natural families 288-289 Diameter of the Mexican Schubertia disticha of Santa Maria del Tule 40i English feet; the sacred Banyan fig-tree of Ceylon almost 30; and the oak at Saintes (Dep. de Ja Charente Inferieure) 29i English feet. The age of the oak tree estimated from its annular rings at from 1800 to 2"lloo years. The root of the rose tree growing against the crypt of the Cathedral at Hildesheim is 800 years old. A kind of sea-weed, Macrocystis pyrifera, attains a length of 630 English feet, exceeding therefore the height of the loftiest Coniferre, even that of the Sequoia gigantea . 289- 291 Examination of the probable number of phrenogamous plants hitherto described or preserved in herbariums. Relative numbers. Laws discovered in the geographical distribution of plants. Relative numbers of the great divisions of Cryptogamia to Cotyledonous plants, and of Monocotyledonous to Dicotyledonous plants, in the torrid, temperate, and frigid zones. Elements of arithmetical botany. Number of individuals; predominance of social plants. The forms of organic beings are rnutu al~y dependent on and limit each other. If we know exactly the number of species of one of the great families of Glumacere, Leguminosre, or Compositre, at any one part of the globe, we may infer approximatively both the number of species in the remaining families, and the entire number of phrenogarnous plants in the same district. Application of the numerical ratios to the direction of the isothermal lines. Mysterious original distribution of types. Absence of Roses in the southern, and of Calceolarias in the northern hemisphere. Why has our heather (Calluna vulgaris)i and why have our oaks never advanced eastward beyond the Ura Mountains into Asia 1 The vegetation cycle of each species requires for its successful organic development a certain minimum amount of temperature . 291- 303 Analogy between the numerical laws of the distribution of animal and of vegetable forms. If there are now cultivated in Europe above 35 000 species of phrenogarnous plants, and if our herbariums probably contain, described and undescribed, from 1601000 to 2121000 species of phrenogamous plants, it is probable that the number of collected insects and collected phrenogamous plants are nearly |