LIST OF ILLUSTRATIONS. 



XI 



PAGE. 



Plate 18. 



A. Lodgepole pine seedlings, all 3 years old, 



but differentiated by the competition 



of Vacdnium, Long's Peak, Colorado 74 



B. Dominance of yellow pine {Pinus pon- 



derosa) and intense competition of 

 lodgepole pine (P. murrayana), Estes 



Park, Colorado 74 



Plate 19. 



A. Competition for light: Piceaengelmannii 



somewhat suppressed by Populus 

 tremuloides, Uncompahgre Plateau, 

 Colorado 76 



B. Competition for water: Boutelova domi- 



nating Grindelia and Gutieirezia by 

 preventing water penetration, Akron, 



Colorado 76 



Plate 20. 



A. Initial invasion at two levels, Pinus 



ponderosa and plains grassland. Black 

 Forest, Eastonville, Colorado 78 



B. Invasion of Agropyrum scnhTieri by 



groups into bare sand. Mount Gar- 

 field, Pike's Peak, Colorado 78 



Plate 21. 



A. Reaction by the accumulation of plant 



remains in water ; peat beds, " Burton 

 Lake," Lancashire, England 82 



B. Reaction by causing weathering. Pilot 



Knob, Halfway, Colorado 82 



Plate 22. 



A. Reaction upon wind-borne material, 



dunes of the Rio Grande, Albuquer- 

 que, New Mexico 86 



B. Reaction by adding humus, Honley 



Wood, Lancashire, England 86 



Plate 23. 



A. Reaction by preventing weathering, 



crustose lichens. Picture Rocks, 

 Tucson, Arizona 88 



B. Consocies of Chrysothamnus reducing 



water erosion in marginal gullies of 

 bad lands, Scott's Bluff, Nebraska . . 88 

 Plate 24. 



A. Reaction by decreasing water-content, 



Grindelia in moister depressions and 

 trails, where it is replaced by Boute- 

 loua, Akron, Colorado 90 



B. Reaction by increasing water-content, 



Polanisia trachysperma in a sand- 

 draw, Crawford, Nebraska 90 



Plate 25. 



A. Peat-bog with Thuja occidenialis and 



Dryopteris thelypteris, Meadowlands, 

 Minnesota 92 



B. Reaction upon light, Pimis murrayana 



consocies, Long's Peak, Colorado ... 92 

 Plate 26. 



A. Stabilization in water, Bidens, Poly- 



gonum, and Jussiaea, French Camp 

 Slough, Stockton, Cahfornia 98 



B. StabiUzation of shifting sand by Sietiersia 



iurbiruUa, Mount Garfield, Pike's 

 Peak, Colorado 98 



PAGE. 



Plate 27. 



A. Ceanothus consocies surrounded by Pinus 



ponderosa climax, which replaces it as 

 a result of competition for light, 

 Spearfish Canon, Black Hills, South 

 Dakota 102 



B. Juniperus and Quercus-Cercocarpus scrub 



colonizing a wind-swept limestone 

 ridge without an intervening grass 



stage, Colorado City, Colorado 102 



Plate 28. 



A. Initial stages of a xerosere, lichens, 



mosses, and liverworts. Picture 

 Rocks, Tucson, Arizona 104 



B. Initial stage of a hydrosere, Nymphaea 



polysepala, in Two Ocean Lakes, 



Yellowstone Park 104 



Plate 29. 



A. Medial stages of a pond sere, sedges, 



grasses, and perennial herbs (Senedo) , 

 Old Faithful, Yellowstone Park 104 



B. Medial stage of a gravel-sUde sere, peren- 



nial herbs, grasses, and imdershrub 

 (Arctostaphylvs) , Crystal Park, Mani- 



tou, Colorado 104 



Plate 30. 



A. Climax prairie of Slipa and Agropyrum, 



Winner, South Dakota 106 



B. Climax forest of Pseudotsuga, Tsuga, and 



Thuja, Mount Rainier, Washington . 106 

 Plate 31. 



A. Chaparral subclimax due to fire, Del 



Mar, California. Relicts of Pinus 

 torreyana 108 



B. Lodgepole subclimax due to fire. Long's 



Peak Inn, Estes Park, Colorado 108 



Plate 32. 



A. Postclimaxes of scrub (Shepherdia, 



Amelanchier, etc.) and of woodland 

 (Vlmus, Fraxinus, Quercus macro- 

 carpa) in prairie climax. Gasman 

 Coulfee, Minot, North Dakota 110 



B. Sagebrush preolimax (Artemisia trideiv- 



tcUa) and Pinus ponderosa climax, 



Estes Park, Colorado 110 



Plate 33. 



A. Zones of Deschampsia, Sdrpus, and 



Pinus murrayana, Nez Perc6 Lake, 

 Yellowstone Park 112 



B. Zones of meadow (Monarda), scrub, and 



woodland. Gasman Coulee, Minot, 



North Dakota 112 



Plate 34. 



A. Alternation of north and south slopes, 



Minnehaha, Colorado. The north 

 slope is covered with the climax 

 forest of Pseudotsuga, the south with 

 Quercus scrub and Pinus woodland . . 116 



B. Rubus layer. Thuja plicata consociation, 



Cedar Mountain, Moscow, Idaho. . . 116 

 Plate 35. 



A. Forest association, Pinus-Abies-hylium 



(P. ponderosa, P. lambertiana, A. 

 concolor), Yosemite, California 126 



B. Scrub association, Artemisia^Sarcobatus- 



halium (A . tridentata, S. vermiculatus) , 

 Fallon, Nevada 126 



