All the wood rangers have noticed, with reference to the immense virgin forests which still cover a considerable extent of the soil of the New World, that, to the man who attempts to penetrate into one of these mysterious retreats which the hand of man has not yet deformed, and which preserve intact the sublime stamp which Deity has imprinted on them, the first steps offer almost insurmountable difficulties, which are gradually smoothed down more and more, and after a little while almost entirely disappear. It is as if Nature had desired to defend by a belt of thorns and spikes the mysterious shades of these aged forests, in which her most secret arcana are carried out.
Many times, during our wanderings in America, we were in a position to appreciate the correctness of the remark we have just made: this singular arrangement of the forests, surrounded, as it were, by a rampart of parasitic plants entangled one in the other, and thrusting in every direction their shoots full of incredible sap, seemed a problem which offered a certain degree of interest from various points of view, and especially from that of science.
It is evident to us that the circulation of the air favours the development of vegetation. The air which circulates freely round a large extent of ground covered with lofty trees, and is driven by the various breezes that agitate the atmosphere, penetrates to a certain depth into the clumps of trees it surrounds, and consequently supplies nourishment to all the parasitical shrubs vegetation presents to it. But, on reaching a certain depth under the covert, the air, less frequently renewed, no longer supplies carbonic acid to all the vegetation that covers the soil, and which, through the absence of that aliment, pines away and dies.
