MARYLAND WEATHER SERVICE 29 



The only methods by which it is possible to obtain any notion of 

 the relation of natural vegetation to soils and other conditions are to 

 select for study areas which have long been undisturbed, and to dis- 

 regard the occurrence of such plants as are tolerant of a wide diver- 

 sity of conditions. To the last-named class belong the majority of 

 our weeds, which indeed owe the fact of their being weeds to this 

 very characteristic, together with their powers of seed production and 

 dissemination. The pin-suit of these methods over as large an area 

 as an entire state renders it possible to draw at least some broader 

 conclusions, which will be found throughout the following pages. 



Together with the scientific aim of presenting a picture of the 

 vegetation of Maryland and its distribution, the present work has 

 been carried on with a view to discovering relations between the 

 natural vegetation and the crop possibilities of definite areas. That 

 such a relation might be expected to exist follows naturally from the 

 fact that spontaneous vegetation and cultivated crops on the same 

 soil in the same place are subject to identical climatic conditions and 

 closely similar conditions of soil. That such a relation actually 

 exists has been shown in a few well-marked cases. The tracing of 

 relations between natural vegetation and cultivated crops is rendered 

 extremely difficult by two sets of considerations. The first of these 

 is the disturbance of the natural vegetation which has taken place, to 

 which allusion has already been made. The second is the fact that 

 the tillage, drainage, fertilization and other processes of treatment id' 

 cultivated land, may often go so far toward making a radical change 

 of soil texture or of the water and food content of the soil as to insure 

 the success of a crop to which the area was at first not adapted. The 

 more marked the physical conditions of a habitat are, the more dog- 

 matic may one be in interpreting its crop possibilities. The less 

 marked are the conditions, that is the nearer they come to the opti- 

 mum for the great generality of plants, the more difficult it is to draw 

 conclusions of other than very general bearing. These matters are 

 taken up more in detail in Part IV. 



The succeeding pages of the Introduction are devoted to a brief 

 presentation of those features of the Climatology, Topography, 

 Mineralogy and Soils of Maryland which are of importance in de- 

 termining the distribution of plant species and plant communities. 



