gradient, 164 



in distribution of species, 116 

 morphological, 131 

 physiographic, 131 

 snow-field, 157 

 Pediculans canadensis (Lousewort), 128 

 Penicillium notatum (Mold), 37 

 Pennsylvania, 33, 163 

 Pensternon parryi (Pink penstemon), 88 

 Perennial ryegrass. See Lolium 

 Periodicity, 77, 85-90, 119, 173 

 Permanence of communities, 158, 159, 



164 

 Phacelia bipinnatifida (Phacelia), 80 

 Phalaridetum arundinaceae association 

 (Reed canarygrass association), 

 180 

 Phanerophyte, 94 

 Phases, vegetation, 166 



downgrade, 139, 153, 155, 162 

 upgrade, 139, 155, 162, 165 

 Phenology, 20, 28, 85, 90 

 Phenotype, 15, 27, 92,96 

 Phippsia algida (Phippsia), 34, 58 

 Photosynthesis, 1 



Phragmitetum communis iowenses associa- 

 tion (Reed association), 180 

 Physocarpus monogynus (Ninebark), 185 

 Physiognomy, 66, 67, 121, 141, 142, 

 159, 177, 185-186 

 and pattern, 130-132 

 basis of classification of communi- 

 ties, 171, 173, 177, 186 

 definition, 130 

 Physiography, 132, 181, 186 

 Phytocenose, 66 



Phytodecta americana (Defoliating bee- 

 tle), 52 

 Phytoedaphon, 93 

 Phytoplankton, 93 

 Phytosociology, 66 

 Picea (Spruces) 



engelmamu (Engelmann S.), 84, 187; 

 mariana (black S.), 84; sitchensis 

 (Sitka S.), 150 

 Pinus (Pines), 37, 38 



banksiana (jack P.), 84, 150; cananen- 

 sis (Canary P.), 43; canbaea (slash 

 P.), 24; contorta var. murrayana 



(lodgepole P.), 41 ; edulis (pinyon), 

 187; jeffreyi Jeffrey P), 13; 

 palustris (longleaf P.), 35; ponde- 

 rosa (ponderosa P.), 13, 137, 183, 

 184, 187; resinosa (red P.), 28, 64; 

 silvestris (Scotch P.), 17, 62; stro- 

 bus (eastern white P.), 62; virgini- 

 ana (scrub P.), 155 

 Pinyon. See Pinus edulis 

 Pitcher plant {Sarracenia flava), 65 

 Plantago (Plantains, Indian wheats) 

 argyrea (I. w.), 88; elongata (slender 

 P.), 144; purshii (wooly I. w.), 84 

 Plasticity, 8 

 Pleistocene, 56 

 Poa (Bluegrasses), 47, 88, 97, 98 



alpina vivipara (viviparous alpine B.), 

 34; bulbosa (bulbous B.), 41; ma- 

 crantha, 149; pratensis (Kentucky 

 B.), 15, 35, 48, 97, 98; pratensis 

 (Merion strain), 5 1 ; secunda (Sand- 

 berg B.), 98, 104 

 Point-contact method, 103 

 Point-observation plot, 103 

 Pollination, 27, 38 

 Polygons in vegetation, 158 

 Polygonum (Knotweeds) 



erectum (erect K.), 144; viviparum 

 (alpine Bistort), 16 

 Polytnchum (Moss), 84 

 Ponderosa pine. See Pinus 

 Ponderosa pine zone, 163 

 Poore, M. E. D., 173 

 Population 



and ecological amplitude, 48 



and genetic homogeneity, 24, 41, 42 



and habitat, 137, 140 



and number of individuals, 43, 100, 



160, 163 

 changes in, 140, 166 

 definition, 1 

 Population density, 78, 100-101 

 and frequency, 113, 116-117, 118 

 and herbage area, 103 

 and volume, 111-112 

 Populus (Poplars) 



sargenlii (Great Plains cottonwood), 

 41; tremuloides (aspen), 40, 41, 53 

 Polentilla sterilis (Cinquefoil), 181 



Inaex • 213 



