The great diversity of the chemical combinations that plants, instead of applying for their proper growth, store up in their tissues as a means of protection against the heat of the sun, the lower fungi, or animals, is really astonishing. Even in the liverworts we meet different substances neither the chemical nature nor the biological importance of which is clearly enough known. Among the ferns, only the under-ground stems are endowed with substances of strong qualities. Only single groups among the monocotyledonous plants, and of these the leaves (Araceæ) or the flowers (Melanthaceæ, lilies) of which show a higher organization, possess acrid poisons or alkaloids or aromatic substances. Among the conifers and dicotyledonous plants the strong substances are very widely diffused in the more enduring kinds.
We have not considered the coloring-matters and odors of the flowers and fruits in this sketch, for they do not serve for protection, but to attract animals.
It is worthy of remark that plants which produce particular substances may be naturalized in regions in which those substances are not required by them. The labiates and rues, which originally belonged to hot climates, still produce ethereal oils in Northern and Central Europe, although they no longer need protection against the hot sun. Closer reflection on the facts we have set forth will show that the real relation must be properly presented as a whole.
Numerous observations, nevertheless, are still necessary in individual cases to make the true significance of each particular phenomenon clear.—Kosmos.
|THE TOPMOST COUNTRY OF THE EARTH.|
THE name Thibet, as we call that highland, the natural isolation of which gives it a unique position in the world, is not known among the people who inhabit it. The Thibetans call their country Bod, or Bod-yirl; the inhabitants of the northern slopes near the great desert call it Tungut; the Chinese, Si-fan. The highland proper rises in the form of a huge elongated segment of a circle from the adjacent lowlands, and is formed by Nature herself, through the sharply denned rocky precipices that inclose it on every side, into a separate part of the world. The country is bordered on the south by the heaven-aspiring crests of the Himalayan system, consisting of three nearly parallel ranges, the southernmost of which forms the real roof of the Thibetan highland. Impenetrable tropical woods rising from the fever-breeding forest and swamp lands are met at a considerable height by the pine-growths, the whole forming a wonderful panorama; above these rise