DEPARTMENT OF BOTANICAL RESEARCH. 97 



overcomes their tendency to grow erect and they trail over the surface, 

 producing numerous branches which repeat the process, soon forming 

 a mat which is the first step in the fixation of the dune. Franseria 

 bipinnatifida is also an important pioneer, but its branches are diageo- 

 tropic from the first, and it therefore stabilizes flat surfaces instead 

 of first building hillocks. The second stage includes a number of semi- 

 pioneers, the most important being Mesenibryanthemum cequilaterale, 

 Abronia umbellata, Convolvulus soldanella, Nemacaulis denudata, Cro- 

 ton calif ornicum, all trailing or decumbent plants which render the 

 dune surface more stable. Oenothera viridescens and Chrysopsis sp., 

 decumbent and matted, or erect and open, according to conditions, 

 characterize the third stage. The second line of succession begins with 

 the salt marsh. Spartina sp. is the pioneer, growing in dense pure 

 masses along the inner edge of the spit. Salicornia ambigua char- 

 acterizes the second stage, and is followed by Frankenia grandiflora 

 and the mat-forming grass Monanthochloe littoralis. The sifting-in of 

 sand brings another community, dominated by Isocoma vernonioides. 

 These two successional lines, having progressed to the points indicated, 

 exhibit a strong tendency to merge, in that a final set of plants appears 

 indifferently in both. None of these is a strictly coastal species, and 

 several belong to the community which an incomplete study points to 

 as the climax of the region around San Diego and southward along 

 the Mexican coast. Among these are Ephedra californica, Yucca 

 mohavensis, Eriogonum fasciculatum, Atriplex canescens, Rhus inte- 

 grifolia, Echinocactus sp., Opuntia occidentalis, Adolphia californica, 

 Encelia californica. 



June, July, and August were devoted to the Monterey region. Here 

 there are three localities where dunes have developed upon a con- 

 siderable scale. The town of Carmel is built mainly upon an estab- 

 lished dune complex of uncertain thickness which mantles a slope of 

 older materials. The succession here has attained to a much more 

 advanced stage than at Coronado, since the sand has blo^vn inland far 

 enough to be free from the retarding influences associated with the 

 immediate shore, and since the history has been an actually longer one. 

 The stages represented are as follows: (1) Abronia latifoUa (corre- 

 sponding roughly to A. maritima of the south); (2) semi-pioneers, 

 including Poa douglasii, Eriogonum latifolium, Abronia umbellata, Me- 

 senibryanthemum cequilaterale, Croton californicum, Oenothera cheiran- 

 thifolia, Convolvulus soldanella, Artemisia pycnocephala; (3) a nearly 

 closed community dominated by Ericameria ericoides, in which Erio- 

 gonum parvifolium, Lupinus chamissonis, and Eriophyllum stcechadi- 

 folium are also important; (4) chaparral, made up of Adenostoma 

 fasciculatum, Arctostaphylos pumila, A. vestita, Ceanothus rigidus, and 

 C. dentatus; (5) forest of Pinus radiata and Quercus agrifolia. The 

 sand-dune succession has here plainly attained to the climax. 



