According to an estimate based on the number of the annual rings, there are yews (Taxus baccata) of from 2600 to 3000 years old. Whether in the temperate northern zone that part of a tree which faces the north has narrower rings, as Michael Montaigne asserted in 1581? Gigantic trees, of which some individuals attain a diameter of above 20 feet and an age of several centuries, belong to the most opposite natural families—pp. [273]–274.

Diameter of the Mexican Schubertia disticha of Santa Maria del Tule 43, of the oak near Saintes (Dep. de la Charente inf.) 30 feet. The age of this oak considered by its annual rings to be from 1800 to 2000 years. The main stem of the rose-tree (27 feet high) at the crypt of the church of Hildesheim is 800 years old. A species of fucus, Macrocystis pyrifera, attains a length of more than 350 feet, and therefore exceeds all the conifera in length, not excepting the Sequoia gigantea itself—pp. [274]–276.

Investigations into the supposed number of the phanerogamic species of plants, which have hitherto been described or are preserved in herbariums. Numerical ratios of plant-forms. Discovered laws of the geographical distribution of the families. Ratios of the great divisions: of the Cryptogamia to the Cotyledons, and of the Monocotyledons to the Dicotyledons, in the torrid, temperate, and frigid zones. Outlines of arithmetical botany. Number of the individuals, predominance of social plants. The forms of organic beings stand in mutual dependence on each other. If once the number of species in one of the great families of the Glumaceæ, Leguminosæ, or Compositæ, on any one point of the earth, be known, an approximative conclusion may be arrived at not only as to the number of all the phanerogamia, but also of the species of all remaining plant-families growing there. Connection of the numerical ratios here treated on in the geographical distribution of the families, with the direction of the isothermal lines. Primitive mystery in the distribution of types. Absence of Roses in the southern, and of Calceolarias in the northern zone. Why has our heath (Calluna vulgaris), and why have our Oaks not progressed eastwards across the Ural into Asia? The vegetation-cycle of each species requires a certain minimum heat for its due organic development—pp. [273]–287.

Analogy with the numeric laws in the distribution of animal forms. If more than 35,000 species of phanerogamia are now cultivated in Europe, and if from 160,000 to 212,000 phanerogamia are now contained, described and undescribed, in our herbariums; it is probable that the number of collected insects scarcely equals that number of phanerogamia; whereas in individual European districts the insects collected preponderate in a threefold ratio over the phanerogamia—pp. [287]–291.

Considerations on the proportion borne by the number of the phanerogamia actually ascertained, to the entire number existing on the globe—pp. [291]–295.

Influence of the pressure of atmospheric strata on the form and life of plants, with reference to Alpine vegetation—pp. [295]–296.

Specialities on the plant-forms already enumerated. Physiognomy of plants discussed from three different points of view: the absolute difference of the forms, their local preponderance in the sum total of the phanerogamic Floras, and their geographical as well as climatic dispersion—pp. [296]–346. Greatest height of arboral plants; examples of 223 to 246 feet in Pinus Lambertiana and P. Douglasii, of 266 in P. Strobus, of 300 feet in Sequoia gigantea and Pinus trigona. All these examples are from the north-western part of the New Continent. The Araucaria excelsa of Norfolk Island, accurately measured, rises only from 182 to 223 feet; the Alpine palms of the Cordilleras (Ceroxylon andicola), only 190 feet—pp. [322]–324. A contrast to these gigantic vegetable forms, presented not merely by the stem of the arctic willow (Salix arctica, two inches in height,) stunted by cold and exposure on the mountains, but also in the tropical plains by the Tristicha hypnoides, a phanerogamic plant which is hardly three French lines (quarter of an inch) in height, when fully developed—pp. [324]–325.

Bursting forth of blossoms from the rough bark of the Crescentia Cujete, of the Gustavia augusta, from the roots of the Cacao tree. The largest blossoms borne by the Rafflesia Arnoldi, Aristolochia cordata, Magnolia, Helianthus annuus—p. [348].

The different forms of plants determine the scenic character of vegetation in the different zones. Physiognomic classification, or distribution of the groups according to external facies, is from its basis of arrangement entirely different from the classification according to the system of natural families. The physiognomy of plants is based principally on the so-called organs of vegetation, on which the preservation of the individual depends; systematic botany bases the classification of the natural families on the consideration of the organs of reproduction, on which the preservation of the species depends—pp. [348]–352.

ON THE STRUCTURE AND MODE OF ACTION OF VOLCANOS IN DIFFERENT PARTS OF THE EARTH—pp. [353]–375.