568 KEPORT OF STATE GEOLOGIST. 



social perennial herbs such as Ammophila and Asclepias obtain a foot- 

 hold, these are followed by shrubs like Cornus, Salix and Prunus, 

 which gradually drive out the former plants, which are not adapted 

 to the shade. The shrubs are followed or accompanied by tree-forms, 

 especially in our area, by the basswood Tilia Americana, with the ap- 

 pearance of the trees, vegetation becomes more and more abundant, 

 and the plant forms become of a more decided mesophytic cast. It is 

 impossible in this connection to do more than to select a few types of 

 established dunes, which may be taken to be fairly representative of 

 our lake shore regions. The three selected are the Basswood, Ever- 

 green and Oak dunes. The obvious condition which favors the rich 

 development of plants is the almost complete protection from the 

 wind. 



PLANTS OF THE MIDDLE BEACH. 



Cakile edentula (Bigel.) Hook (==G. Americana Nutt.) American Sea- 

 rocket. The character plant of the middle beach. 

 Euphorbia polygonifolia L. Spurge. 

 Corispermum hyssopifolium L. Bug-seed. 



The distribution of these plants is not at all uniform over the middle 

 beach. Their favorite place for growth is along the line of debris which 

 marks the upper limit of this beach. This limit is variable from year to 

 year, depending partly upon the number and violence of the storms, 

 more definitely upon the advance or recession of the lower beach. 



PLANTS OF UPPEE STKETCHES OF BEACH. 



Populus balsamifera candicans (Ait.) Gray. Balm of Gilead. Rare. 



Lathyrus maritimus (L.) Bigel. Beach Pea. 



Thalesia fasciculata (Nutt.) Britton. (=Aphyllonfasciculatum A. Gray.) 



Root parasite on the Artemisias. 

 Artemisia caudata Michx. Wormwood. 

 Artemisia Canadensis Michx. 



Both species of Artemisia are abundant, being the dominant form at 

 times over extended areas. The most characteristic species. 

 Carduus Pitcheri (Torr.) Porter. (=Cnicus Piteheri Torr.) 



This thistle, while seldom so common as Artemisia, is pretty sure to be 

 found on any upper beach. 



Certain plants, especially characteristic of embryonic dunes, are found, 

 though rarely in great abundance, upon the upper stretches of the beach. 

 Among these are Ammophila arenaria, and Elymns Canadensis. Calama- 

 grostis longifolia, one of the chief character plants of active dunes, is also 

 sometimes found in this locality. Cakile edentula and Corispermum hys- 



