Note 34 — LAMARCKIAN HYPOTHESIS OF THE ORIGIN OF PLANTS. ITS CONSEQUENCES.

The following digest from Professor Balfour’s very admirable “Manual of Botany,” of what is held on this curious subject, may be not unacceptable to the reader. “It is an interesting question to determine the mode in which the various species and tribes of plants were originally scattered over the globe. Various hypotheses have been advanced on the subject. Linnæus entertained the opinion that there was at first only one primitive centre of vegetation, from which plants were distributed over the globe. Some, avoiding all discussions and difficulties, suppose that plants were produced at first in the localities where they are now seen vegetating. Others think that each species of plant originated in, and was diffused from, a single primitive centre; and that there were numerous such centres situated in different parts of the world, each centre being the seat of a particular number of species. They thus admit great vegetable migrations, similar to those of the human races. Those who adopt the latter view recognize in the distribution of plants some of the last revolutions of our planet, and the action of numerous and varied forces, which impede or favor the dissemination of vegetables in the present day. They endeavor to ascertain the primitive flora of countries, and to trace the vegetable migrations which have taken place. Daubeny says, that analogy favors the supposition that each species of plant was originally formed in some particular locality, whence it spread itself gradually over a certain area, rather than that the earth was at once, by the fiat of the Almighty, covered with vegetation in the manner we at present behold it. The human race rose from a single pair; and the distribution of plants and animals over a certain definite area would seem to imply that the same was the general law. Analogy would lead us to believe that the extension of species over the earth originally took place on the same plan on which it is conducted at present, when a new island starts up in the midst of the ocean, produced either by a coral reef or a volcano. In these cases the whole surface is not at once overspread with plants, but a gradual progress of vegetation is traced from the accidental introduction of a single seed, perhaps, of each species, wafted by winds or floated by currents. The remarkable limitation of certain species to single spots on the globe seems to favor the supposition of specific centres.”