502 THE POPULAR SCIENCE MONTHLY. 



ing up the accumulated stores of combined nitrogen in the soil 

 are quite as significant factors in the nutrition of leguminous 

 plants as their symbiont microbes that appropriate free nitrogen ; 

 and the conditions of soils and plants that determine the exer- 

 cise of these diverse biological activities, in one direction or the 

 other, present a promising field for future investigation. With 

 every advance in knowledge there is increasing evidence that the 

 transformations of matter and energy taking place in the normal 

 processes of living organisms are so exceedingly complex that 

 they can not be expressed or defined in simple formulae relating 

 to a single department of science, and this fact must be recognized 

 if any real progress is made in solving the problems presented in 

 the applications of science to agriculture. 



THE ARYAN QUESTION AND PREHISTORIC MAN. 



Br Peof. T. H. HUXLEY. 

 II. 



AT the present time, four great separate bodies of water, the 

 Black Sea, the Caspian, the Sea of Aral, and Lake Balkash, 

 occupy the southern end of the vast plains which extend from 

 the Arctic Sea to the highlands of the Balkan Peninsula, of Asia 

 Minor, of Persia, of Afghanistan, and of the high plateaus of 

 central Asia as far as the Altai. They lie for the most part be- 

 tween the parallels of 40 and 50 north, and are separated by 

 wide stretches of barren and salt-laden wastes. The surface of 

 Balkash is five hundred and fourteen feet, that of the Aral one 

 hundred and fifty-eight feet above the Mediterranean ; that of 

 the Caspian eighty-five feet below it. The Black Sea is in free 

 communication with the Mediterranean by the Bosporus and the 

 Dardanelles ; but the others, in historical times, have been at 

 most temporarily connected with it and with one another, by 

 relatively insignificant channels. This state of things, however, 

 is comparatively modern. At no very distant period, the land of 

 Asia Minor was continuous with that of Europe, across the pres- 

 ent site of the Bosporus, forming a barrier several hundred feet 

 high, which dammed up the waters of the Black Sea. A vast 

 extent of eastern Europe and of western central Asia thus became 

 a huge reservoir, the lowest part of the lip of which was probably 

 situated somewhat more than two hundred feet above the sea- 

 level, along the present southern water-shed of the Obi, which 

 flows into the Arctic Ocean. Into this basin the largest rivers of 

 Europe, such as the Danube and the Volga, and what were then 

 great rivers of Asia, the Oxus and Jaxartes, with all the inter- 



