Page:Popular Science Monthly Volume 29.djvu/460

444  dry will last for many hundreds of years, as has been the case in the roofs of foreign buildings, or when it is submerged in the water, as has been the case of piles used for foundations of the earlier bridges in older countries. Posts and telegraph-poles can daily be seen which are decaying near the ground-line, but sound above, after three to four years' service. By comparing the different conditions of use, it can be seen how little change is required to render unstable what would be stable under other circumstances. In roofs, the conditions are dryness, circulation of air, plenty of spores, and sufficient temperature to germinate, but the necessary moisture is absent. In the case of submerged piles, plenty of water, sufficient temperature, but exclusion of air, either to carry spores or permit them to grow. In the case of the posts and telegraph-poles we have the spores, the moisture, and the necessary temperature in summer for germination, and decay ensues from the fact that these are the essential conditions for the growth of the fungi whose work it is to undo and liberate the compounds in the woody tissue.



.—The relations of the United States to Mexico naturally group themselves under two heads—political and commercial.

The political relations of the United States with Mexico, whether the people or the Government of the former wish it or not, are going to be intimate and complex in the future. The United States is geographically married to Mexico, and there can be no divorce between the parties. Intercommunication between the two countries, which a few years ago was very difficult, is now comparatively easy, and facilities for the same are rapidly increasing. And with the rapid increase of population in the United States, and with increased facilities for travel, the number of people—restless, adventurous, speculative, or otherwise minded—who are certain to cross the borders into Mexico for all purposes, good and bad, is likely to rapidly increase in the future. An extensive strip of territory within the Mexican frontier is already dominated, to a great extent, for the purposes of contraband trade, by a class of men who acknowledge no allegiance to any government, and whom the Mexican authorities tacitly admit they can not restrain. Out of such a condition of things political complications between the two countries, at no distant day, are almost certain to arise.