312 Annals of the Carnegie Museum. 



At Presque Isle this formation is characterized by Cakile edentula 

 and Xanthium commune, together with the minor species : Euphorbia 

 polygonifolia, Strophostyles helvola and Cenchrus carolifiianus. The 

 plants are scattered along here and there, in the line of driftwood, 

 there being no particular localization of species, except that the 

 Xanthium and Strophostyles occur more abundantly in the sheltered 

 places, or in places where the driftwood is more abundant. This, in 

 Xanthium at least, is probably due to the character of the disseminule, 

 the burs of Xanthium in exposed places being liable to washing away 

 by the waves, or blowing away by the wind. The most efficient 

 method of dissemination in this habitat is a combination of wind and 

 wave, the floating disseminules being cast upon the beach among the 

 driftwood and there left buried in the sand, ready to grow the next 

 season. 



Along the drift-beach at Cedar Point, Sandusky, the habitat is 

 characterized by Cakile, Xanthium and Polanisia graveolens, the last 

 named being more abundant along the lake-beach while the Xanthitttn 

 is more partial to the more protected bay-beach. Along Lake Michigan 

 Cowles found the habitat characterized by Cakile, Corispermum hyssopi- 

 foliuin and Euphorbia polygonifolia, the first named species being gen- 

 erally the most prominent. He mentions Strophostyles helvola as an 

 inhabitant of the narrow beach at the base of sea-cliffs, but it has " not 

 been seen as yet on the beaches of the dune district. ' ' ^^ Ganong finds 

 Salsola Kali, Cakile, Mertensia inaritima and a few other species on 

 the drift -beach at Miscou Island, New Brunswick, Cakile being second 

 in abundance to Salsola "though but scarce." ^" 



Kearney in his studies in the Dismal Swamp region " and on 

 Ocracoke Island*^ calls attention to the extremely strong insolation, 

 the periods of intense heat, and the strong currents of air, which 

 together constitute the xerophytic conditions, to which the plants are 

 there exposed on the strand, and which in connection with the un- 

 stable condition of the soil are met by certain adaptations in the life- 



*' Cowles, H. C. "The Physiographic Ecology of Chicago and Vicinity." fiot. 

 Gaz., 31 : 170, March, 1901. 



<f Ganong, W. F. /. c, pp. 85-87. 



*' Kearney, T. H. "Report on a Botanical Survey of the Dismal Swamp Region. ' ' 

 Contrib. U. S. Nat. Herb., V, 367-395, 1901. 



*^ Kearney, T. H. "The Plant Covering of Ocracoke Island." Contrib. U. S. 

 Nat. Herb., V, 275-284, 1900. 



