148 
The sensitiveness of Juniperus virginiana to fire, a natural 
consequence of its thin bark,* has been commented on in some 
of the general works cited below, if not elsewhere; but the 
geographical significance of this fact seems never to have been 
pointed out before. 
The various habitats of the cedar are protected from fire in 
different ways. Marshes and estuarine swamps are usually too 
wet for fire to travel through, and on dunes and rocks (the latter 
including the cedar-glades) the herbaceous vegetation is too 
sparse to feed flames. The exemption of pastures and fence- 
rows from fire is too obvious to require any further comment. In 
the Florida hammocks, as in other climax forests, the humus 
does not burn readily, partly because it is usually too damp, and 
partly because most of the carbon in it is already oxidized.T 
The abundance of cedar on limestone rocks may now be partly 
explained by the fact that such rocks are most extensively 
exposed in the interior hardwood region and in other regions 
which. were characterized originally by vast climax forests and 
now by cultivated fields, where forest fires from natural causes 
are and always have been very infrequent, apparently. It is 
possible, however, that a little lime in the soil may be advan- 
tageous to our tree, for it seems to be entirely absent from the 
fall-line sand-hills and stream sand-hills of the coastal plain, 
which are almost exempt from fire but decidedly non-calcareous; 
while the dunes on the coast must contain appreciable quantities 
of calcium carbonate in the form of comminuted sea-shells. 
Furthermore, outside of the glaciated region Juniperus Virginiana 
seems rarely or never to associate with any of the Ericaceae, a 
family of plants noted for their preference for acid soils. T Never- 
* Its usually shallow root-system has been suggested as another factor which 
makes the cedar an easy prey to fire; but it would be hard to find a tree with shal- 
lower roots than Pinus Caribaea where it grows on limestone rocks southwest of 
Cocoanut Grove, кещ and that species is almost immune to fire. The cedar 
usually ишсе near the ground, and that is probably another reason why it is 
T In this connection see Bull. Torrey Club 38: gai IQII. 
{Та this connection see Hilgard, Soils 522. 1906; Coville, U. S. Bureau of 
Plant у Bull. 193: 19, 30. 1910; Harper, Ann. Rep. Fla. Geol. Surv. 3: 361. 
I9II. 
