MAKYLAND WEATHEE SEKVICE 299 



Spruce and the Buckwheat, that the soil requirements of the two 

 correlated species are quite distinct. 



The other inquiries mentioned above may be made as respects the 

 vegetation of smaller areas with uniform climate, when the mat- 

 ter of topography and soils becomes the centre of interest. The 

 composition of forests is of particular value in indicating the char- 

 acter of soils because it represents the degree to which the component 

 species find their optimum requirements. It is, in other words, a 

 special case of the indicating value of individual species, in which 

 natural competition has served to bring forth into predominance the 

 species to which the conditions are most nearly suited. 



The greatest obstacle to using forest composition as an index of 

 agricultural capabilities is one that also hindered the gathering of 

 an adequate idea of the original forest covering of the various por- 

 tions of the state, namely marked difference between nearby forests 

 under identical external conditions. The conditions under which 

 each particular piece of woodland was cleared and under which it 

 has returned to forest have a great and a varying influence on its 

 make-up. Particularly in the Lower Midland District on the Cecil 

 loam and the Cecil mica loam do the forests vary in composition to 

 an extreme degree. Elsewhere, as in Worcester County, the same 

 type of forest may be found on a number of the different soil types 

 recognized. Indeed, a comparison of the soil map of Worcester 

 County with the carefully prepared forest map will show at a glance 

 that there is no sharp relation between the soils and the forest types. 

 It is true, however, that many soils which are mapped as distinct are 

 differentiated on characters that are of no importance in the physi- 

 ology of the plant, as for example, the Cecil loam and the Cecil 

 mica loam, the Sassafras sandy loam and the Portsmouth sandy loam. 

 In the case of soils of more marked character there are, however, 

 obvious differences in the plant covering, as occurs in the Lower 

 Midland District between Cecil loam and Susquehanna gravel, or 

 either of these soils and the Conowingo clay, or between Norfolk 

 sand and Elkton clay. The physiography of an area is of determ- 

 ining influence upon the plant covering through its fundamental 

 relation to soil water supply, and this fact offsets many influences 

 of soil composition, as may be noted in the difference between the 



