FLOWERING PLANTS AND PEBNS OF INDIANA. 



III. The Upper Beach. 



This is the part of the beach beyond the reach of the waves. "The 

 life conditions are much less severe than on the middle beach, chieflv 

 because of the freedom from the wave action of the winter storms. 

 The exposure to the sun is almost as great as on the lower zones, but 

 there is more protection from the wind because of the abundance of 

 driftwood. The decay of the driftwood may also add no inconsider- 

 able portion to the food material of the beach plants. 



"The flora of the upper beach is much richer than that of the middle 

 beach, both in species and individuals, but here as there the vegetation 

 is so sparse that the tone to the landscape is given by the soil." 



IV. The Active Dunes. 



Neglecting some very interesting phases in the life history of 

 dunes, touching upon their embryonic stages and the plants concerned 

 in fixing them and passing also their transformation into wandering 

 dunes, we may consider the conditions in this active dune which is 

 usually a part of what Dr. Cowles denominates the dune complex. The 

 factors involved give, of course, to the complex great instability, but it 

 is very evident that in this shifting maze plant life must be very scant. 

 "The reasons for the scanty plant life on the exposed portions of the 

 dune complex are not far to seek. First of all it is not due to the scar- 

 city of water in the soil. Even after a long period of drought in sum- 

 mer, the sand is cool and moist at a short distance below the surface. 

 In spite of the water supply in the dune sand, the scanty flora of the 

 complex is characterized by the possession of the most pronounced 

 xerophytic adaptations to be found in this latitude. In the' main these 

 adaptations are to guard against excessive transpiration, such as is 

 induced by unusual exposure to wind, heat and cold. 



"Directly or indirectly, the wind is the factor primarily responsible 

 for the scant vegetation of the dune complex." While incidentals the 

 wind dries up the soil and increases transpiration, and while its me- 

 chanical action in connection with the sand blast is destructive to 

 vegetation, its cardinal destructive influence lies in its power to cover 

 and uncover the dune plants. 



V. The Established Dunes. 



In time the slowly advancing slopes of the dune complex may be 

 captured by vegetation and be transformed into an established dune. 

 The story of the capture is wonderfully interesting, when followed in 

 its details. Briefly stated the stages are something like this. First, 



38-Geol. 



