396 HARPER: BOTANICAL CROSS-SECTION OF MISSISSIPPI 
the character of the flora of northern Mississippi is the prevalence 
of clayey soils, contrasting strongly with the sand of the pine- 
barrens nearer the coast. Sand is here chiefly confined to the 
beds of creeks and rivers, as it is in most of the interior hardwood 
region. The character of the soil may not be wholly independent 
of the seasonal distribution of rainfall, but it would be too much 
of a digression to discuss the matter here. Suffice it to say that 
it happens that in the Eastern United States most regions with 
wet winters and dry summers have fertile clayey soils, and where 
the reverse is true sandy soils predominate. 
Some relations of vegetation to soil chemistry. Dr. Hilgard, in 
his earliest and latest books (1860 and 1906), and in various other 
works, has always stressed the importance of chemical composition 
of soil, especially the percentage of lime, in determining the 
character of the vegetation. In his ‘‘Soils,’’ page 490, as already 
noted, he gives the lime percentages for each soil belt of northern 
Mississippi, and describes the corresponding vegetation briefly. 
Similar correlations have been made in Europe by a number of 
investigators, and the fertility of calcareous soils has been long 
proverbial. Limestone is one of the commonest and most easily 
recognized minerals, so that such correlations are easily made; 
but in the light of the observations made on this trip, and other 
recent investigations, it is highly probable that some of the other 
mineral ingredients of soils which do not manifest themselves so 
conspicuously may be equally important to vegetation. 
In the case of lime there always has been a difference of opinion 
as to just how much of it a soil should contain to be called cal- 
careous. According to Dr. Hilgard, in Europe a soil is not usually 
called calcareous unless it effervesces with acid, which requires 
about 5% of lime (calculated as CaO)*; while in this country 
many soils containing only 1% of lime differ as much in their 
vegetation from those which have less as they do from some derived 
from nearly pure limestone. He concludes that calcareous soils 
are distinguished better by their vegetation than by any arbi- 
trary chemical stahdard; but here another difficulty is encoun- 
tered. Just what is calciphile vegetation? ; 
Various European investigators, Schimper} for example, have 
* In this connection see Plant World 15: 300-301 
T See pages 94-106 of his Plant roam de English aes 1903. 
