BARRIERS TO FOREST EXTENSION 83 
northern regions, such as the Adirondacks, coppice- 
growth is slight. In many parts of this country the 
pines have been replaced by the broad-leated species. 
THE DESERT OF UTAH. 
Showing lack of vegetation and wind erosion. 
In the total absence of moisture a desert results. 
Some species, after long years of hardship, have be- 
come inured to a scarcity of moisture, especially the 
cacti, the leaves of which are thorns and the stems of 
which have developed into leaf-like structures. These 
stems are storehouses of moisture, and the thorns are 
a protection against the greedy animals of the desert. 
The date is a very valuable tree, which is able to with- 
