428 



PLANT SOCIOLOGY 



Pinus, strobus, 109 



forest, 143, 333 

 Pioneer communities, 309, 352, 371 



stages, 17, 320 



trees, significance of, 330 



vegetation, 308, 330 

 Piper, 296 

 Pirola chlorantha, 66 



minor, 120 



secunda, 90 



uniflora, 59, 66, 67, 68 

 Pirus, 280 

 Pistacia atlantica, 9 



lentiscus, 8, 130, 273 

 Plankton, 75 



chamber, 75 



communities, 75 



density and dominance of, 75 



periodicity of, 75, 76 



reaction to calcium, 184 



seres, 334 



stratification, 75 

 Plant associations (see Associations) 



communities and pH values, 170 

 historical factor of, 82 

 organic units, 315 

 organization of, 19 

 {See also Communities; Associa- 

 tions; Formation; AlUance; 

 Social units; etc.) 



geography, life forms in, 298 



litter, 245 



migrations, 350 



sociology, fundamental units of, 22 

 primary problems of. 1 

 structure of, 81 

 Plantaginion crassifoliae, 375 

 Plantago coronopus var. maritima, 193 



crassifolia assn., 375 



intermedia, 364 



major, 14, 193 

 Plants, communal relationships of, 5 

 Plasticity, ecologic, 13 

 Plateaus, climate of, 262 

 Platycerium, 296 

 Playas, 199, 200 

 Pleurococcus, 291 

 Pleuston, 370 

 Pluchea sericea, 202 



Poa alpina, 71, 119, 239, 308, 310 



annua, 297 



bulbosa-Onopordon illyricum assn., 

 376 



chaixii, 69 



concinna, 114 



flabellata, 291 



foliosa, 291 



laxa, 308, 310 



nemoralis, 69 

 Podocarpus, 236 

 Podsols, 256, 312 



alpine, 174 



buffering of, 177 



development of, 311 



formation of, 163 



profiles of, 174 

 Podsolization, 314 

 Pogonatum urnigerum, 310 

 Pohlia, 293, 310 



commutata, 122, 308 



nutans, 89 

 Polemonium pulcherrimum, 7, 8, 90 

 Pollen analysis, 337, 340, 351 



and the development of vegetation, 



338 

 methods of, 338 



diagrams, 337 



spectra, 340 

 Polster plants, 292, 293, 307 



(See also Cushion plants) 

 Polygala dunensis, 67 

 Polygonal soil structure, 197, 231 

 Polygonatum multiflorum, 43, 69, 290 



officinale, 68 

 Polygonion, 374 



Polygono-Chenopodion polyspermi, 373 

 Polygonum amphibium, 13 



aviculare, 14 



viviparum, 71 

 Polymorphic groups, 63 

 Polypodion, 373 

 Polypodium vulcanicum, 203 



vulgare, 74, 373 

 Polytrichetum sexangularis, 29, 57, 



110, 121, 136, 137, 190, 263, 310 

 Polytrichum, 309 



alpinum, 310 

 formosum, 69 

 juniperinum, 72 



