Page:Aspects of nature in different lands and different climates; with scientific elucidations (IA b29329668 0002).pdf/340

from 1800 to 2000 years. The root of the rose tree growing
against the crypt of the Cathedral of 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 Coniferæ,
even that of the Sequoia gigantea 94-97

Examination of the probable number of phænogamous 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 mutually dependent on and limit each other.
If we know exactly the number of species of one of the great
families of Glumaceæ, Leguminosæ, or Compositæ, 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
phænogamous 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), and why have our oaks
never advanced eastward beyond the Ural Mountains into Asia?
The vegetation cycle of each species requires for its successful
organic development a certain minimum amount of temperature. 97-113

Analogy between the numerical laws of the distribution of animal and
of vegetable forms. If there are now cultivated in Europe above
35000 species of phænogamous plants, and if our herbariums probably
contain, described and undescribed, from 160000 to 212000
species of phænogamous plants, it is probable that the number of
collected insects and collected phænogamous plants are nearly