42
AGENCY OF MAN IN THE
[Book III.
Why have they not, supposing them to have been everso distinct originally, become more blended and con-founded together in the lapse of ages ?
Agency of man in the dispersion of plants .—But inaddition to all the agents already enumerated as in-strumental in diffusing plants over the globe, we havestill to consider man—one of the most important ofall. He transports with him, into every region, thevegetables which he cultivates for his wants; and isthe involuntary means of spreading a still greaternumber which are useless to him, or even noxious.“ When the introduction of cultivated plants is of recentdate, there is no difficulty in tracing their origin; butwhen it is of high antiquity, we are often ignorant ofthe true country of the plants on which we feed. Noone contests the American origin of the maize or thepotato; nor the origin, in the old world, of the coffee-tree, and of wheat. But there are certain objects ofculture, of very ancient date, between the tropics,such, for example, as the banana, of which the origincannot be verified. Armies, in modern times, havebeen known to carry, in all directions, grain and cul-tivated vegetables from one extremity of Europe tothe other; and thus have shown us how, in moreancient times, the conquests of Alexander, the distantexpeditions of the Romans, and afterwards the cru-sades, may have transported many plants from onepart of the world to the other.”*
But, besides the plants used in agriculture, thenumber which have been naturalized by accident, orwhich man has spread unintentionally, is considerable.One of our old authors, Josselyn, gives a catalogue of