Plant Industries and Climatic Plant Formations 343 



soils are acid, others neutral, and still others are alkaline. The 

 slope of the soil may be so great, or the rocks so near the surface, 

 that cultivation is impossible. 



In other words, within each climatic region there are many 

 plant habitats, some of which may be used for one crop, some for 

 another, and some that are best left to produce pasturage or crops 

 of trees. Consequently, any one crop usually occupies only a 

 part of the climatic region in which it might be grown if the 

 conditions in all localities were favorable. For example, tobacco 

 is one of the most profitable crops of the deciduous forest region ; 

 but since its quality is greatly influenced by soil conditions, its 

 cultivation on a large scale is limited to certain definite soil 

 areas. Moreover, each of these soil areas is given over to the 

 growing of some particular type of tobacco. 



Crop centers. A study of the geography of crop plants will 

 show that each crop has a region in which it is so profitable that 

 a considerable proportion of the suitable land is given over to 

 it. These regions are called crop centers. Moreover, the centers 

 of production of most crops coincide in large measure with the 

 climatic plant formations. Each plant formation has, therefore, 

 become a center of production of a certain group of crop plants. 



In colonial days all the possible crops were grown in every lo- 

 cality. As the West became settled and transportation facilities 

 increased, the several crops were gradually moved into the most 

 favorable regions, and farming in any one locality became more 

 specialized. This movement is still going on and is of great 

 importance for the future supplies of agricultural products. Dis- 

 regarding market factors, those crops are most profitable which 

 best fit both the climate and the soil. As a result of competition 

 among farmers in different sections of the country, the pro- 

 duction of a particular crop at time^ increases in certain localities 

 and decreases in others. 



Crop plants less restricted than wild plants. Crops may be 

 so valuable that the grower can afford to make artificial habitats 



