270 



Ecological Characteristics. — The plants that persist in this as- 

 sociation possess certain general characteristics : ( i ) they are an- 

 nuals, because perennials are uprooted during, the winter storms; 

 (2) their disseminules are comparatively heavy, so that altho they 

 are blown about they are not blown away; (3) their seeds have suf- 

 ficient vitality for sending their tap-roots through 4-10 cm. of dry 

 sand to the moist sand below; and (4) their aerial parts are low, 

 radiately branching" or bushy, narrow-leaved, and frequently succu- 

 lent. In other words, the plants of this association are subjected to 

 the severest kind of xerophytism. Such a habitat, hydrophytic be- 

 neath the surface of the ground and xeropyhtic above ground, is 

 termed dissophytic by Clements. 



Devclopincyit. — In the Beach area the middle beach, to use Cowles' 

 term, exists in two modifications. Towards the southern end, it is 

 highest at the boundary line separating it from the low-er beach, 

 from which it slopes very gradually down to the fringing dune — a 

 slope of but a few centimeters at most. Towards the north the nar- 

 row middle beach slopes upwards and abruptly gives way to the much 

 higher (2-4 meters) fringing dune. Here the middle beach is sub- 

 ject to continual removal of its sand by the prevailing westerly winds. 

 As the winds are in the westerly half of the compass much more than 

 half of the time, the formation of extensive or high dunes is impos- 

 sible on account of the lack of sand. The replenishment of the sand 

 of the middle beach takes place during the easterly storms, of which 

 there are but a few each year. Such storms, as a rule, are accom- 

 panied by i)recipitation, which further retards their power of bring- 

 ing up sand from the lake. One may judge of the amount of sand 

 that such a storm may pile up by the efi"ects of the storm of July 30- 

 31, 1908, in which the wind w'as east for a day and a half. A ridge 

 some 20 meters wide and 0.4 meters high was piled up in front of 

 the mouth of the Dead River, completely closing tlie channel — 6 

 meters wide and 0.5 meters deep — which that river had liad the day 

 previous. And this does not begin to compare with the amounts 

 blown up on the southern and eastern shores of Lake Michigan. Some 

 sand is blown up during the winter unless the shore is ice bound. At 

 that season there is a noticeable transfer of sand from the northern 

 parts, where it is held by the season's vegetation, towards the south- 

 ern parts, where north of the \\'aukegan piers it is building the shore 

 out into the lake. 



The southern part is more wind-swept because protected on the 

 landward side by only a very low (at most 0.2 meters) fringing 

 dune. It is characterized by extreme openness of vegetation. The 



