Page:Popular Science Monthly Volume 46.djvu/414

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atmosphere escapes through, special openings in the epidermis, which are called stomata, or breathing pores. These openings are not visible to the naked eye. Fifty of these stomata may be counted on a square millimetre of leaf surface, and the number sometimes rises to five hundred in the same area. Each leaf is therefore provided with several million such openings. They expand or contract according to the necessity, and the correlation is so well adapted that the width of the opening is regulated so as to agree exactly with the existing conditions. They are usually closed at night, when a strong evaporation is not called for, because the salts which the water carries into the leaf can only be elaborated in the light. The transpiration being diminished at night, besides, by the lower temperature and the increased moisture in the air, the stomata can often remain open at that time without injury. This would be the case, for example, when the breathing process—which is likewise carried on through the stomata—is prolonged. The effect of the light is to open the breathing pores at dawn if they are closed, or to expand them. An increase in transpiration is now wanted, and it facilitates the exchange of gases by the assimilation of carbon. The opening fails to respond to the stimulus of the light if there is not enough water for the demands of the plant, when rapid evaporation would promote wilting. The active mechanisms of the plant react upon the external influences, and are in turn affected by them in the manner most advantageous to the plant at the given moment. The fact that the plant is not able to choose its reactions freely causes these reactions always to occur correctly according to the course of the external conditions.—Translated for The Popular Science Monthly from the Deutsche Rundschau.

The Flora Italiana, begun in 1848 by Filippo Parlatore, and now completed except as to a part of its seventh volume, is, according to Garden and Forest, one of the few floras of large countries or of extensive botanical regions that have come so near their end. The two others of note are Bentham's Flora of Australia and Boissier's Flora of the Orient. The other great floras, including Gray's of North America and Sir Joseph Hooker's of British India, are still unfinished. Notwithstanding the much that has been achieved in learning the characters, relationships, uses, and distribution of plants, our knowledge of them is still fragmentary and often unsatisfactory, and a vast amount of work remains yet to be done by morphological and economic botanists.

"Buckland is persecuted," wrote Baron Bunsen of the eminent geologist to his wife in April, 1839, "by bigots for having asserted that among the fossils there may be a pre-Adamite species. 'How,' say they, 'is not that direct, open infidelity? Did not death come into the world by Adam's sin?' I suppose, then, that the lions known to Adam were originally destined to roar throughout eternity!"