1899] DUNE FLORAS OF LAKE MICHIGAN 385 
sent the normal climax type of the lake region, the deciduous 
forest. 
On the established windward slopes the development is quite 
different from that described above. There is a dominance of 
evergreens instead of deciduous vegetation. The soil condi- 
tions are nearly alike on the two slopes, but the air is more xero- 
phytic on the windward slopes. The evergreen flora starts as a 
heath formed of Arctostaphylos, Juniperus communis, and J. Sabina 
procumbens. The heath arises on fossil beaches, secondary embry- 
onic dunes, or wherever the wind is relatively inactive and where 
the conditions are too xerophytic for the development of a 
deciduous flora. Before long the heath passes into a coniferous 
forest,'in which Pinus Banksiana, P. Strobus, or P. resinosa domi- 
tate. Coniferous forests also occur on sterile barrens and in 
bottoms, where the conditions are also unfavorable for deciduous 
forests. A slight change in the physical conditions may bring 
about the rejuvenation of the coniferous dunes, because of their 
*xposed situation. Rejuvenation commonly begins by the forma- 
tion of a Wind-sweep; the vegetation on either hand is forced 
9 succumb to sand-blast action and gravity. 
The evergreen floras are more and more common northward, 
While to the south there are developed forests in which Quercus 
‘occinea tinctoria prevails. The oak forests are more common on 
inland dunes and on southern slopes. The oaks may follow the 
pines, when the areas occupied by pines become sufficiently pro- 
tected from cold winds. The pines have a much wider range of 
if Conditions than the oaks, since they appear at lower levels, 
Sher levels, and on northern or windward slopes. The oaks 
fourish best on southern slopes. The flora of the oak dunes is 
“tophytic, but of the desert type, while that of the pine dunes 
i. arctic xerophytic type. The pine dunes have a north- 
ora, the oak dunes a southern flora. 
VI. Previous studies of sand dune floras. 
“great deal of physiographic work has been done in 
nm areas in total disregard of the plant life, although the 
sand 
