398 Harper: BOTANICAL CROSS-SECTION OF MISSISSIPPI 
is very little soil on top of it. But almost none of the trees 
regarded as calciphile in the states farther north are found there, 
and the question arises, are the numerous species of trees growing 
on limestone in South Florida (nearly all of them tropical) true 
calciphiles? They are certainly very different in aspect from the 
supposed lime-loving trees of Mississippi, being nearly all ever- 
green. Furthermore, some of the commonest species, the pine 
especially, flourish equally well in sandy soils a little farther north, 
which are very poor from an agricultural standpoint. 
Let us see now if there is not some soil ingredient other than 
lime which is of fundamental importance to vegetation. One of 
the most convenient and at the same time perhaps the most sig- 
nificant characters of arboreal vegetation that can be expressed 
quantitatively is the percentage of evergreens, and this has been 
already indicated roughly for most of the soil belts described above. 
The percentages of certain soil ingredients also have been given, 
and it will be noticed that in the regions under consideration the 
evergreens can be correlated with potash just about as well as with 
lime, evergreens being scarcest in the soils richest in potash. 
This relation is still more apparent when we compare northern 
Mississippi, where nearly all the soils are pretty well supplied with 
potash, with Florida, where soil conditions are very different. 
Florida has a larger proportion of evergreens than any other 
state in the Union, and at the same time its soils are poorest in 
potash, though fairly well supplied with lime.* It is altogether 
likely that the limestones of South Florida above mentioned are 
deficient in potash, though I have too few data on this point as yet. 
Statistics collected by Hilgard in his book on Soils show that the 
‘percentage of potash in tropical soils is usually less than in those of 
‘temperate regions; and it is barely possible that the prevalence 
of evergreens in the tropics may be due partly to this fact, and 
not to climate alone, as has been hitherto supposed. In temperate 
* On page 11 of Bulletin 85 of the U. S. Bureau of Soils, published late in r9t2, 
there is a table of the average chemical composition of the soils of each state, based 
on over a thousand analyses. The average of 88 samples from Florida is 0.03% of 
potash and 0.31% of lime. The corresponding figures for four typical hardwood 
states are as follows: Kentucky, 92 samples, 0.35% potash, 0.18% lime; Ohio, 57 
samples, 0.25% potash, 0.29% lime; Tennessee, 144 samples, 0.28% potash, 0.20% 
lime; West Virginia, 14 samples, 0.53% potash, 0.16% lime. 
