144 MINNESOTA STATE HORTICULTURAL SOCIETY. 



up enough moisture to have fostered the primitive forests with which all 

 that region was covered. The moist air flowing away from the more 

 elevated plain to the west, left that region supplied with air largely 

 from the north, west and south-west. This air, not containing a great 

 amount of moisture, is warmed up and made to absorh rather than pre- 

 cipitate moisture, hence the low humidity of the air, the small rainfall, 

 and the consequent absence of trees on the plains and prairies. The mix- 

 ture of cold and moist winds was facilitated in the eastern part of the 

 valley while in the western part the air was "rarified" so far as humidity is 

 concerned. Of course, 1 have illustrated the workings of the winds in the 

 most general way. As the settlement of this country has crossed the valley 

 of the Mississippi, from the east to the west, considerable change has been 

 wrought in the surface of the land and in the amount of moisture held in 

 reserve to be evaporated into the air. Forests which are great water 

 conservers have been destroyed, especially in the eastern part where most 

 forests existed. In those forests which have been allowed to stand, much 

 of the old-time forest conditions have been destroyed by clearing out and 

 pasturing 1he lands, thus giving the water of rains, formerly held by 

 the decaying leaves, a chance to run off over the surface of the closely 

 packed sod. Sloughs, ponds and even lakes have been drained, and 

 streams also have been relieved of most materials which formerly clogged 

 their rapid flow. The thick matted grass of our prairie has given way to 

 cultivated fields and closely cropped meadows and pastures. The con- 

 dition of the soil in our corn fields, for example, is in such condition as 

 to thoroughly take in the waters of rainfall, because acting like a sponge 

 it draws the water into itself. But these crops are mostly very leafy, 

 usually evaporating it rapidly back into the air, not allowing it to be 

 stored up in the soil and subsoil. The closely shaven and hard soil in our 

 pastures does not readily absorb water, but allows the rainfall to largely 

 run off and eventually reach the great rivers. This is especially facili- 

 tated by systems of artificial drainage. 



Explain it in whatever way we may there is no disputing the fact that 

 the cultivation of new sections of country, prairie as well as wooded lands, 

 immediately lessens the amount of water in the soil and subsoil. Sloughs 

 go dry, ponds and lakes become shallower, or dry up entirely, the ground 

 water sinks as is shown by our being compelled to dig wells deeper ten to 

 twenty "years after settlement begins, in every neighborhood. Even 

 many of the hillside springs which were perennial during the first years 

 the country was occupied dry up, and not a single new one is observed to 

 burst forth. That there is a lessened supply of surplus ground water as 

 the years go on, no intelligent western farmer who has passed twenty or 

 more years in intimate acquaintance with the land in any neighborhood 

 during its complete settlement will deny. Most meteorologists run 

 squarely against a very important fact when they claim that the annual 

 rainfall in the upper Mississippi valley is not being modified by man. 

 While I believe that the main effect on our water supply is in the lessened 

 humidity of the air in the warmer parts of our summers, thus causing 

 more severe drouths, I suspect also that our rainfall is slightly decreasing 

 in the warmer summer months. The supply of conserved moisture nearly 

 gives out and there is not enough to keep up the supply in the air when 

 the atmosphere is warm and able to hold its maximum amount before 



