566 KEPORT OF STATE GEOLOGIST. 



graph of Dr. Cowles 1 and through additional suggestions furnished by 

 him, the materials for this section have been derived. So complete 

 and satisfactory was the study of Dr. Cowles, that previously prepared 

 discussions of this flora have been discarded and his article taken as 

 the basis of the presentation of the subject. 



From the ecologic sub-divisions worked out by Dr. Cowles, the fol- 

 lowing have been selected as fairly representing characteristic condi- 

 tions in the area considered. 



I. The Lower Beach. 



"The lower beach has been denned as the zone of land washed by 

 the waves of summer storms. It might also be denned as that portion 

 of the beach which is devoid of vegetation. Perhaps there is no flora 

 in the temperate zone quite so sparse as that of the lower beach, unless 

 we except bare rocks and alkaline deserts. Land life is excluded be- 

 cause of the frequency and violence of storms; the waves tear away the 

 sand in one spot only to deposit it in another. Even though a seed 

 had the temerity to germinate, the young plant would soon be de- 

 stroyed by the breakers. Water life is excluded because of the extreme 

 Xerophytic conditions, which commonly prevail on the lower beach. 

 Thus the lower beach is a barren zone between two zones of life. Be- 

 low it there exist algae and other hydrophytic forms, which nourish in 

 the fury of the breakers; above it there exists the flora of the middle 

 beach, a, flora adapted to the most intense xerophytic conditions. At 

 no particular time, perhaps, are the conditions too severe for some type 

 of life; vegetation is excluded because of the alternation of opposite 

 extremes." 



II. The Middle Beach. 



"This is situated between the upper limits of the summer and winter 

 waves, comparatively dry in summer, but washed by high waves in win- 

 ter. It may also be defined as the zone of succulent annuals. The life 

 conditions of this zone are exceedingly severe and result in a flora of 

 the most pronounced xerophytic characters." The winter storms pre- 

 clude the possibility of survival through that period, thus practically 

 excluding biennials and perenials. "In the summer time the xeroph- 

 ilous conditions are extreme. Nowhere in the dune regions are the 

 winds more severe than here. No flora is more exposed to the extreme 

 desiccating influences of the summer sun than that which grows upon 

 the bare and open beach." 



'Cowles, H. C. — " The Ecological Relations of the Vegetation of the Sand Dune* of Lake 

 Michigan:' Bot. Gaz., Vol. 27, Nos. 2, 3, 4 and 5. 



