444 THE POPULAR SCIENCE MONTHLY. 



fectly 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 tempera- 

 ture to germinate, but the necessary moisture is absent. In the case 

 of submerged piles, plenty of water, sufficient temperature, but ex- 

 clusion 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 moist- 

 ure, 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. 



-- 



AN ECONOMIC STUDY OF MEXICO. 



By Hon. DAVID A. WELLS. 

 V. 



PRESENT AND FUTURE RELATIONS OF THE UNITED STATES TO 

 Mexico. 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 geo- 

 graphically 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 facili- 

 ties 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 gov- 

 ernment, 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. 



