20 ECONOMIC BOTANY OF ALABAMA. 



mocks, and pine woods, within a region, but not for de- 

 limiting regions large enough to show on a state map. 



Another difficulty th^t is unavoidable in the use for 

 geographical purposes of any one simple factor, such as 

 altitude, or any function of temperature or rainfall, that 

 can vary in only one direction (i. e., from greater to less, 

 or vice versa), is that all zones based on single factors 

 must be parallel, so that each one can touch only two 

 others, as is well illustrated by a hypsometric or climatic 

 map on which the various altitudinal or temperature 

 zones are shaded differently. It is indeed true that in 

 some restricted areas the various types of forest are dis- 

 tributed to some extent in parallel zones; but if any one 

 of these zones is followed far enough it will as a rule be 

 found to narrow down and disappear, or run up against 

 some other zone (there are several examples of both 

 cases on the map of Alabama accompanying this report) ; 

 which can never happen with climatic or altitudinal 

 zones. There are also many forest regions that are about 

 as broad as they are long; so that a true map of forests 

 (or any other kind of vegetation) would look something 

 like a mosaic, or a crazy-quilt. 



Topography and soil are not open to the objection just 

 mentioned, for they are complex features, and may vary 

 in an indefinite number of ways. Topography however 

 does not affect vegetation directly as much as it does in- 

 directly through its influence on the local distribution of 

 soil types, ground-water, and sunlight. Soil is almost 

 universally admitted to be of fundamental importance 

 to vegetation, and soils are comparatively easy to map — 

 after a satisfactory classification for them is devised* — , 

 for the several types are usually distributed in fairly 

 well-defined patches. 



The smaller soil units are too small and too numerous 

 for our present purposes, but it is possible to group them 

 roughly according to certain characters into classes or 

 regions, each large enough to be shown on a state map. 



*For a recent discussion of the pi'oblems of soil classification 

 see E. 0. Fippin, Science 11.35:677-686, May 3, 1912. Also Bulle- 

 tin 85 of the U. S. Bureau of Soils, by G .N. Coffey. November, 

 1912. 



