18 BOTANICAL GAZETTE [SEPTEMBER 
tion of the force of the wind, either on account of the increasing dis- 
tance from the shore as the lake waters recede, or by the building 
up by the wind of high dunes which form a windbreak and protect 
the sand ridges. 
PINE-OAK STAGE.—With the relative cessation of sand move- 
ment, coupled with increase of humus, the pine-oak stages begin. 
As might be expected, the content of vegetation on the ridges shows 
a certain amount of progressive change, both in floristic content 
and in the density of growth and mesophytism, as we traverse the 
Fic. 8. iF of old pine, oak, and hemlock, probably protected by proximity 
to Platte Rive 
region from the vicinity of the lake toward the south (that is, from 
younger to older ridges). On the first ridges there is a preponder- 
ance of conifers and many relics of the herbaceous pioneers, especi- 
ally Artemisia, Smilacina stellata, Arctostaphylos, and Juniperus 
spp. The first tree of this stage to come into the coniferous asso- 
ciation of the open dunes is Pinus Strobus, followed shortly by 
P. resinosa. Quercus ellipsoidalis, Q. alba, and possibly Q. velutina 
follow rather slowly, and now may be found fairly evenly distributed 
in the more advanced portions of the area. Acer rubrum is very 
frequently met near Platte River, or in other somewhat moist 
