474 BOTANICAL SURVEY OF DISMAL SWAMP REGION. 



the premises from which deductions were to be drawn. As will pres- 

 ently be seen, this very lack of diversity, while removing some diffi- 

 culties from the survey, was an obstacle to obtaining very striking 

 results. 



COMPARATIVE INFLUENCE OF DRAINAGE AND CHEMICAL 



FACTORS. 



In the Dismal Swamp region, if we consider only lands that give 

 some promise of agricultural value, variations in drainage constitute 

 the mosl important soil differences. In other parts of the country 

 chemical composition of the soil plays a leading part. For example, 

 limestone and freestone soils are often very sharply differentiated 

 within a limited area. Such differences are of little importance in the 

 country we are considering. Only the salt-marsh and sand-dune 

 soils, and those of the fresh-water wooded swamps previous to being 

 drained, present important peculiarities in their chemical composi- 

 tion. Needless to say, these three formations are worthless from an 

 agricultural point of view, so long as they remain in their natural 

 condition. Omitting them from the discussion, the problem becomes 

 chiefly one of water content, depending in great part upon the fineness 

 of subdivision exhibited by the soil. When this is coarse, the soil is 

 sandy and well drained. When finely divided, it becomes silly or 

 clayey, holding water longer and in greater quantity. 



Now the respective characteristics of vegetation upon a sandy well- 

 drained soil and upon clayey wet land are much less striking, and 

 the transition from one to another is more gradual and less easy to 

 define than is the case where important chemical differences exist. 

 The line between vegetation that grows in a soil rich in lime and that 

 upon a lime-poor soil is often so abrupt and sharply defined as to be 

 easily recognizable at a distance. Not only size, habit, hairiness, etc., 

 differ markedly in the same species when growing upon one or the 

 other kind of soil, but there are a number of species which prefer 

 limestone soils, while others show a strong aversion to soil that con- 

 tains much lime. Thus the systematic makeup of the vegetation 

 changes to a large extent as we pass from one soil to the other. 1 



1 1n the United States the distribution tit' plants upon soils rich or poor in lime 

 (which means chiefly calcium carbonate. CaCO.J has not received the attention 

 which it deserves. Undoubtedly interesting results await the student of this 

 important problem in soil chemistry and plant geography. Jn Europe much work 

 has been done in the line indicated. Especially in France the matter has been 

 approached from the standpoints of chemistry, physics, and geology, as well as of 

 botany. The agricultural journals, and writers upon forestry, have devoted much 

 space to its consideration. Several attempts have been made to segregate the 

 indigenous plants of various regions as confined to limestone soilB. preferring 

 lime, preferring freestone, confined to freestone, or indifferent. Bonnier and 

 others have indicated, however, that a hard and fast classification is not easily 

 attainable, as species which are "lime-loving'" in one chain of mountains are 



