298 THE PLANT LIFE OF MARYLAND 



ing in that spot or in what relation it stands to the plants with 

 which it is associated, it would appear at first thought that the 

 introduced weeds are quite as good indicators of the conditions of 

 soil or climate under which they are persisting as are the native 

 species. This is a matter in which both native and introduced plants 

 vary among themselves, but in general it may be said that the great 

 bulk of native plants are capable of survival only in much narrower 

 ranges of conditions than are the introduced ones which have become 

 weeds. 



An inquiry into the relation between spontaneous and cultivated 

 vegetation may well follow several lines of procedure. To what ex- 

 tent, it may be asked, do the ranges of occurrence of native species 

 indicate the regions in which particular crops may be successfully 

 planted ; to what extent does the composition of the forest give indi- 

 cations; to what extent the occurrence of particular tree species in 

 the forests ; and, as well, to what extent may the occurrence of par- 

 ticular weeds or other herbaceous plants serve the same end. 



Correspondences have frequently been pointed out between the 

 natural range of a plant species and the area within which a partic- 

 ular crop may be successfully planted. For example, I have been 

 told by Dr. Koland M. Harper that in the southern states there is a 

 close correspondence between the distribution of the Loblolly Pine 

 and that of the profitable cultivation of cotton, and in Maryland the 

 region in which the Red Spruce is native is adapted to the success- 

 ful cultivation of buckwheat. These are cases in which it is the 

 length of growing season and the temperature requirements of the 

 correlated species that is significant. Merriam has pointed out-'" 

 the various life zones of the United States, based upon the collective 

 ranges of characteristic plants and animals, and has shown that 

 these may furnish a basis for recommendations as to the probable 

 success of various cereals, vegetables and fruits within the zones. 

 This class of phenomena is quite a special case in the relation of 

 natural and cultivated plant life, and can give only the most general 

 indications with regard to the suitability of the atmospheric factors 

 affecting plants. Indeed, it often happens, as in the case of the 



*Merriani, C. Hart. Life Zones and Crop Zones of the United States. 



