544 POPULAR SCIENCE MONTHLY. 



general in making them more soluble in the ground waters, and thus 

 more available to plant nutrition. 



It will thus be seen that it is possible to control, in a measure, the 

 soil. In another way much has been done in controlling soil and soil 

 conditions, and that is in controlling the climate above the soil. This 

 climate, or condition of the atmosphere above the soil and in contact 

 with it, is also a most important factor in the growth and develop- 

 ment of plants, and any way in which this can be controlled, correspond- 

 ingly can the development of the plants be controlled. This is familiar 

 to every one in the use of frames, hot-houses and conservatories, and, in 

 some of the modern structures of this kind, it can hardly be said that 

 the method is one adapted to a small scale only. In illustration, atten- 

 tion might be called to an establislmient in Ehode Island which has 

 upwards of fourteen acres under glass for the cultivation of one crop 

 alone. And this can hardly be regarded as an isolated instance. 

 Many others as extensive, or perhaps even more extensive, might be 

 cited. In the last few years an even more striking illustration, because 

 much greater in extent, of this control of climate has been developed in 

 this country. For this purpose as well as for some other reasons, enor- 

 mous areas in Florida are covered with either slats or cloth tent-like 

 arrangements. These are erected for the purpose of protecting the 

 plants and developing abnormal or unusual growth in certain varieties 

 of tobacco, and have proved immensely successful in prolonging the 

 growing season, through a modification of the climate about the plant, 

 keeping it moist and warm, not cutting off the light entirely, but par- 

 tially, and preventing the great evaporation from the surface which 

 would dry the soil, and hasten the ripening of the plant. The experi- 

 ment has been repeated in Connecticut under the auspices of the Bureau 

 of Soils, U. S. Department of Agriculture, in cooperation with the 

 Connecticut Experiment Station, over a very considerable area, some- 

 times single fields of as much as eight acres in extent being now pro- 

 tected by these cloth coverings for the production of a high-grade 

 wrapper leaf tobacco. The shading of one crop by another with a taller, 

 umbrageous growth, is a similar procedure. And this is practiced quite 

 extensively in some places, as in the shading of coffee trees by larger 

 tree growths, or the more familiar nurse crops, common in some parts 

 of the United States. Modifications of the climate in other ways, by 

 planting of trees, erection of wind brakes, and devices of a similar 

 nature, have been used with greater or less success in certain regions, 

 and are all more or less well known. 



It is thus possible to greatly modify the soil and the soil conditions. 

 Nevertheless the fact remains that it is impossible to make one soil just 

 like any other soil. Consequently characteristic differences do exist in 

 them, and it follows that some soils are adapted to some purposes for 



