I have deemed it expedient to indicate the different points of view from which the laws of the distribution of vegetable forms may be considered. It is only when these points of view are confounded together, that we meet with contradictions, which have been unjustly attributed to uncertainty of observation.[NL] When expressions like the following are employed: “This form, or this family diminishes as it approaches towards the cold zone,” or “the true habitat of this form is in such or such a parallel of latitude;” or “this is a southern form,” or, again, “it predominates in the temperate zone;” it should be definitely stated whether reference is made to the absolute number of the species, and the proportion of their predominance according to the increase or decrease of latitude; or whether the meaning conveyed is, that a family, when compared with the whole number of the phanerogamia of a flora, predominates over other families of plants. The impression conveyed to the mind of the predominance of forms, depends literally on the conception of relative quantity. Terrestrial physics have their numerical elements as well as the cosmical system, and it is only by the united labours of botanical travellers that we can hope gradually to arrive at a knowledge of the laws which determine the geographical and climatic distribution of vegetable forms. I have already observed that in the temperate zone of the northern hemisphere, the Compositæ (Synanthereæ) and the Glumaceæ (in which latter division I place the three families of the Gramineæ, the Cyperoideæ, and the Juncaceæ) constitute the fourth part of all phanerogamia. The following numerical relations are the result of my investigations for seven great families of the vegetable kingdom in one and the same temperate zone: Glumaceæ ⅛ (Grasses alone ¹⁄₁₂) Compositæ ⅛ Leguminosæ ¹⁄₁₈ Labiatæ ¹⁄₂₄ Umbelliferæ ¹⁄₄₀ Amentaceæ (Cupuliferæ, Betulineæ, and Salicineæ) ¹⁄₄₅ Cruciferæ ¹⁄₁₉