1899] DUNE FLORAS OF LAKE MICHIGAN 383 
Small dunes are formed in more protected places by plants’ 
that are unable to exist on the beach, or where there is rapid 
dune formation. Among these secondary dune-formers are 
Andropogon, Arctostaphylos, Juniperus. Primary embryonic 
dunes may pass gradually into this second type, as this latter 
passes into the heath. 
The stationary embryonic dunes on the beach begin to wander 
soon as the conditions become too severe for the dune-forming 
pants. The first result of this change is seen in the reshaping 
of the dune to correspond with the contour of a purely wind- 
made form. The rapidity of this process is largely deter- 
mined by the success or failure of the dune-formers as dune- 
lolders. The best dune-holders are Calamagrostis, Ammophila, 
and Prunus, 
There are all gradations between a simple moving dune 
md a moving landscape; the latter may be called a dune- 
‘omplex, The complex is a restless maze, advancing as a whole 
7 one direction, but with individual portions advancing in all 
thections. It shows all stages of dune development and is 
forever changing, The windward slopes are gentle and are 
‘ittowed by the wind, as it sweeps along; the lee slopes are 
mt steeper. The only plant that flourishes everywhere on the 
eee is the succulent annual, Corispermum hyssopifolium, 
‘though Populus monilifera is frequent. The scanty flora is not 
toe to the lack of water in the soil, but to the instability of the 
‘il and to the xerophytic air. es 
The influence of an encroaching dune upon a preexisting 
" Varies with the rate of advance, the height of the dune 
= country on which it encroaches, and the nature of the 
fee The burial of forests is a common phenomenon. 
“dominant forest trees in the path of advancing dunes Pe 
ay pintsiana, Quercus coccinea tinctoria, and Acer ee 
b ot these trees are destroyed long before they are completely 
as the dune 
is The dead trees may be uncovered later, 
ce °n beyond. 
‘the Dune Park region there are a number of swamps upon 
