380 



THE STUDY OF PLANT COMMUNITIES 



Mutual relationships— Continued 



energy cycle, 12 



food, 12 



to environment, 27 

 Mycorhiza, 26, 194-195 



and alkaline conditions, 195 



ectotrophic, 194-195 



endotrophic, 194-195 



of orchids, 195 

 Myrica calif ornica, 281 



cerifera, 52, 257, 259 

 Myriophyllum, 175 



N 

 Natural resources 



can be conserved and used, 316 



communities and environments, 

 315 



forests, 316-321 



range, 321-326 



soil, 326-336 



water supplies, 341-344 



wildlife, 345 

 Natural thinning, 24 

 Neocalliergon integrifolium, 303 

 Nitrate fixation, 196-197 



algae, 197 



bacteria, 196-197 

 Nitrogen in soil 



fixation, 196-197 



product of decomposition, 197 

 Nodules 



legumes, 196 



nitrogen fixation, 196 



on leaves. 196 



soil fertility, 196 

 Nolina, 290 

 Nyssa aquatic a, 258 



biflora, 258 



sylvatica, 254 



O 



Oak-chestnut association, 251-252 

 Oak-hickory association, 222, 252- 

 255 

 fire and swamp subclimaxes, 255- 

 259 

 Oak-hickory forest, 222 



day and night temperatures, 127 

 stratification, 25 

 vernal aspect, 25 

 Oak-mountain mahogany climax, 



268-269 

 Oenothera hiimifiisa, 51, 52 

 Ohieya, 288 



Opuntia, 268, 288, 297 



arborescens, 67 



inerviis, 207 

 Organisms 



mutual relationships, 12 



reactions on environment, 212-213 

 Original vegetation, land surveys, 53 

 Overgrazing, 42, 355, 356 

 Overstocking, forest, 24 

 Oxalis montana, 241 

 Oxydendrum arboreum, 254 

 Oxyria digyna, 239 



Pacific conifer forest, 276, 277, 278- 

 280 



montane zone, 276-280 



northern part, 279 



range, climate, altitudes, 276 



southern part, 279 



subalpine zone, 276 

 Paleo-ecology 



fossil evidence, 302 



interglacial relicts, 302, 303 



methods, 301-302 



stratification of peat, 303-304 

 Panicum virgatwn, 292, 293 

 Pantograph, in use, 39 

 Papaver spp., 239 

 Parasites, 26 



beetles, borers, 26 



chestnut blight, 190 



community structure, 190 



dodder (Cuscuta), 191 



Dutch elm disease, 190 



moths, 26 



witches brooms, 191-192 

 Pasture indicators, 355-357 

 Pasture problems, 333-336 



planting, 334-335 



woodlots, 333 

 Peat bogs, 258-259 



development, 216 

 Peat deposits, 302-303 



drained and cultivated, 209 



pollen analysis, 304-307 

 Peat sampler, 304 

 Pedalfer, 157-158 

 Pedicularis semibarbata, 272 

 Pedocal, 156, 157-159 

 Percolation under litter, 127 

 Periodicity 



aspect dominance, 65 



in deciduous forest, 67 



leaf fall, 68, 143 



