196 BOTANICAL GAZETTE [MARCH 
enlarged, another has passed from existence without leaving a 
trace behind. Where a dune was advancing last year, there is 
now, perhaps, a hollow swept out by the wind. Where last 
year was a hollow there may now be seen the beginnings ofa 
flora, or again the flora of a former year may have been buried 
out of sight. The dune-complex, then, is not only a maze, but 
also a restless maze. 
branches 
formed of 
Fic. 7.—Trough-shaped wind-sweep at Beaver island. Dead roots and 
of plants that have been torn up. Embryonic dunes in the background 
sand brought from the foreground. Sparse annual vegetation in the wind-sweePp: 
eads of 
It might seem impossible to unravel the tangled thr 
details 
the dune-complex; it is, indeed, impossible to write the 
of its history. There is, however, a simplicity in the complexity 
While little dunes advance in all directions, the complex ose 
whole advances in the direction of the prevailing wind. Whi 
there are troughs at all angles, the main troughs are ike 
the direction of the wind. The complex is like a river with! 
