The Ecological Relations of the Vegetation on the Sand Dunes of Lake Michigan. Part I.-Geographical Relations of the Dune Floras.

FEBRUARY response to varying conditions. Plant formations should be found which are rapidly passing into other types by reason of a changing environment. These requirements are met par excellence in a region of sand dunes. Perhaps no topographic form is more unstable than a_ dune. Because of this instability plant societies, plant organs, and plant tissues are obliged to adapt themselves to a new modeof life within years rather than centuries, the penalty for lack of adaptation being certain death. The sand dunes furnish a favor-| able region for the pursuit of ecological investigations because of the comparative absence of the perplexing problems arising from previous vegetation. Any plant society is the joint product of present and past environmental conditions, and perhaps the latter are much more potent than most ecologists have thought. | | DUNE FLORAS OF LAKE MICHIGAN 97