386 



THE STUDY OF PLANT COMMUNITIES 



Soil, water constants— Continued 



permanent wilting percentage, 



169-170 

 readily available water, 1 70 

 wilting coefficient, 169 

 evaporation loss, 165-166 

 infiltration, 163 

 loss by transpiration, 166 

 measurements, 172-174 

 content, 172 



electrometric methods, 173 

 expression of, 172 

 forces with which held, 172 

 of variations, 172 

 physical forces, 173 

 sampling and weighing, 1 72 

 soil point cones, 173 

 tensiometers, 173 

 weight versus volume basis, 

 172 

 movement, 163-165 

 origin, 162-163 

 weathering, 144 

 well, 146, 147-148 

 Solstices, 116-117 

 Sonoran desert, 287, 288 

 Sorbus americana, 63 

 Sorghastrimi nutans, 292, 293 

 Space (occupied), 61-62 

 clipping and weighing, 62 

 estimation of volume, 62 

 relation to basal area, 62 

 Spartina pectinata, 292 

 Species : area curve, 45, 47 

 Spectrum, 118 

 Sporobolus cryptandrus, 293, 295 



heterolepis, 292, 293 

 Stand, 21,22,23, 45 

 Stipa, 268 



eomata, 293, 295, 297 

 leucotricba, 293 

 pulchra, 297 

 spartea, 292, 293, 295 

 Stipulicida setae ea, 257 

 Stomatal activity, 135-136 

 response to drought, 136 

 response to light, 135 

 Strangers (fidelity), 72 

 Stratification, 22, 25, 66 

 and dependent species, 23 

 and dominance, 23 

 and layer communities, 25 

 and sampling, 65 

 causes, 22 

 diagrams, 65 



dependence, 26 



light, 132 



sampling methods, 48 



studied with bisects, 54 



subordinate species, 23 



synusia, 25 

 Stratification-cover diagrams, 65, 66 

 Stream margins, 330 

 Street lights 



photoperiod, 142 



winter killing of trees, 142 

 Subalpine forest 



Rockies, 261-263 



Sierra Nevada, 270, 271-274 

 Subclimax, 226 

 Subordinate species, 23 

 Succession 



after fire, 242 



causes, 212-214 



concept, 212 



historical background, 211-212 



in old fields, 221-222 



kinds, 214-216 



primary and secondary, 213-214 



quantitative studies, 231, 232, 233 



rate, 221-223 



stabilization and climax, 223-224 

 Successional diagram, 213 

 Sun leaves 



characteristics, 137-139 



where found, 137 

 Sunspot activity 



climate and tree growth, 310 

 Swamp 



forests, 258-259 



succession, 217 



vegetation, 217 

 Symbiosis, 193-196 



mycorhiza, 194-195 



nodules, 195-196 

 Sy?nphoricarpos spp., 269 



rotundifolius, 272 

 Synecology, defined, 17 

 Synthetic characteristics, 69-74 



coefficient of community, 74 



Constance, 71 



fidelity, 72 



presence, 69, 70, 71 

 Synusia, 25 



forest floor, 23-24 



T 



Taiga, 240 



Tall grass prairie, 291-292-294 



Talus, 150-151 



