J. D. Dana on the Origin of Prairies. 301 
a. Elms, maples, and other shade trees drop their fruit pro- 
fusely over a grass-covered lawn, and yet none take root. Ihe 
grass prevents the seeds for the most part from reaching the 
soil; or if washed into it by rains, the pre-occupation by the 
grass hinders their development. | 
6. But along the sides of an earth-made path, and in shaded 
places, as near a fence or hedge, a crop of young plants will 
often spring up. 
the sh osition is one favorable for perpetuated 
Moisture, and those which fall into the open and enriched soil 
of a garden, will stand the usual summer’s drou nd live. 
1 pra regions, ? 
reason—the stratification of the alluvium; over many prairie 
vail throughout the year along some sea-coasts, an 
