CHAP. LXX DISTRIBUTION 271 



produce a forest, where poplar, oak, ash, walnut, sassafras, and other 

 trees occur, and are festooned with numerous lianes, such as Celastrus 

 scandens, Vitis cordifolia, Rhus Toxicodendron, Ampelopsis quinquefolia, 

 and Smilax hispida. Shrubs are frequent in open places and at the 

 margin of the forest. In addition to the original shrubs many other 

 species settle. The majority of the species in the dune-forest are defi- 

 nitely mesophytes. On the windward side annual and biennial herbs 

 are the first to germinate, and among them Corispermum hyssopifolium 

 leads the way. In the course of time small shrubs arise and produce 

 scrub 1 composed of Arctostaphylos Uva-ursi, also Juniperus Sabina and 

 J. communis. Scrub in turn gives way to coniferous forest composed 

 of Pinus Strobus, P. Banksiana, P. resinosa, Thuya occidentalis, Abies 

 balsamea, and Juniperus virginiana. Beneath the trees grow shrubs 

 belonging to the dune-scrub. In the shade many mosses thrive. On 

 dunes lining the shores of Lake Michigan bushland composed of Quercus 

 coccinea partly replaces coniferous forest. 



In Virginia and North Carolina, according to Kearney, 2 the earliest 

 sand-fixing species are Psamma arenaria, Uniola paniculata, Panicum 

 amarum, and Iva imbricata, which belongs to the Compositae. Farther 

 from the beach the dunes are covered by grassland composed of Psamma 

 and Panicum, between which grow shrubs of Myrica carolinensis, Quercus 

 virginiana, and Rhus copallina. The oldest dunes are clothed with 

 pine-forest. 



The dunes of Nebraska are occupied by the following sand-binding 

 grasses : Calamovilfa longifolia, Redfieldia flexuosa, Eragrostis tenuis, 

 Muehlenbergia pungens, and many others. 3 



In sandy parts of northern Mexico (in the Tularosa desert) there occur 

 dunes in which Yucca radiosa is the most important sand-fixing plant. 

 Its roots extend horizontally for a distance of forty feet from the shoot. 

 Two grasses (Andropogon and Sporobolus), a few shrubs and undershrubs, 

 and many annual herbs, comprise the remainder of the vegetation. 4 In 

 the Tularosa desert the shifting sand is not composed of silica, but of 

 gypsum. 5 



South America. In South America psammophilous vegetation occurs 

 on the coast, but there are also enormous tracts of sand and immense 

 dunes in the interior of Chile, 6 and of the Argentina. 7 In the latter there 

 grow not only a number of kinds of grasses, including Cenchrus, Diachyrium, 

 and Bouteloua, but also other plants which, for the most part, are appar- 

 ently aphyllous and include the zygophyllaceous Bulnesia Retamo, a 

 true psammophyte which often sets a limit to the advance of the sand, 

 species of Ephedra and Cassia, Mimosa ephedroides, and the boraginaceous 

 Cortesia cuneifolia. In the Argentine Andes Fries 8 distinguishes a 

 Lampaya-association and a Patagonium arenicola-association. 9 



1 Which Cowles terms ' heath '. * Kearney, 1901. 



3 Rydberg, 1895. * Coville and MacDougal, 1903. 



5 In regard to North American dunes and their oecology, special reference 

 should be made to the works of Rydberg, 1895 ; Coville, 1893; Cowles, 1899; 

 Kearney, 1901 ; Pound and Clements, 1898 ; Hitchcock, 1 904 ; and Harshberger, 

 1900, 1902. 



6 F. Albert, 1900. 7 Brackebusch, 1893. " R- E. Fries, 1905. 

 9 Respecting the oecology of dunes in New Zealand the works of Diels, 1 896, and 



Cockayne, 1904, should be consulted. 



