RECENT BOTANY AND GENERAL DISTRIBUTION 



PLANTS OF ARKANSAS, 



GENERAL REMARKS. 



The distribution of the plants of a country, according to the nature of 

 its geological formations, is extremely difficult to settle with any chances 

 of reliability. It has been asserted with apparent reason : 



1st. That it is still uncertain if the chemical elements of the soil, even 

 if it was proved that they are directly depending on the nature of the 

 underlying geological strata, have a perceptible influence on the vegeta- 

 tion which naturally covers any peculiar place. That, in any case, the 

 amount of influence which the chemical constitution of the soil exercises 

 upon the distribution of the vegetation is still problematical. 



2d. That the geological elements, viz., the particles resulting from the 

 decomposition of the rocks and entering into the composition of the soil, 

 even if their influence on the vegetation were well marked, are generally 

 disseminated by water and atmospheric agency to a great distance from 

 the areas occupied by the formations from which they come. The lime 

 of a limestone ridge, the sand of a mountain of sandstone are carried 

 down the declivities, spread over other kind of rocks, transported to the 

 alluvial plains, or deposited on the banks of rivers and thus mixed toge- 

 ther in a peculiar compound which, in its new state, has but an indirect 

 relation to the rocks from which it is derived, and -no relation whatever to 

 the formations which it covers. Moreover, the frequent alternations of 

 strata of sandstone and of limestone which compose the rocks of the great 

 Valley of the Mississippi, Silurian, Devonian, Carboniferous, and Tertiary, 

 prevent an exact limitation of the area over which each of them may 

 extend its influence. Thus, it has been generally admitted that physical 

 circumstances more actively govern the distribution of the vegetation of a 



