258 



INDEX 



Plant materials, kinds of, added to 



soil, 76 

 Plant nutrients, 14-18 

 Plant substances, classification of, 

 76-77 

 composition of, 76-79 

 Plants, absorption of nutrients by, 17 

 influence of composition of, on 

 decomposition, 91-92, 133, 

 146 

 on bacterial numbers in soil, 189- 



191 

 on carbon dioxide evolution from 



soil, 186-187 

 on nitrification, 145 

 on soil microbes, 224 

 on soil processes, 182-186 

 proximate composition of, 78, 79 

 relation of microbes to, 45 

 variation in composition of, with 



growth, 78, 79 

 water-soluble constituents of, 77, 

 79 

 Plants and microbes, 181-202 

 Plasmodiophora brassicae, control of, 



221 

 Plate method, 52-55 



for determination of fungi in soil, 68 

 Podsol soil, composition of, 3 

 Population of the soil, 41-42, 44-74 

 Potassium, availability, Aspergillus 

 niger method, 238, 240 

 in plant nutrition, 14, 15 

 in soil, 16, 18 



transformation of, by microbes, 

 178-180 

 Potato scab, control, 231-232 

 Proteins, 78 



decomposition of, 49, 90, 91, 126- 



129, 131 

 nature of, 126-127 

 Protista, 24 



Protozoa, effects of partial steriliza- 

 tion on, 225, 227-228 

 in soil, 23, 38-39, 69-70, 71 

 nutrition of, 39 

 Protozoan theory, 227-228 

 Pure cultures of microbes, 24 



Putrefaction, 30 

 Pythium, 41 



R 



Raw humus, formation of, 205-206 

 soils, activity of fungi and bacteria 



in, 82 

 nitrogen transformations in, 139 

 Reaction, influence of, on cellulose 

 decomposition, 83-86 

 on microbial development, 63-64 

 on nitrification, 137-142 

 on nitrogen fixation, 111-113, 

 124-125 

 Reaction of soil, 17 

 influence of, on soil microbes, 220- 



221 

 influence of lime on, 217-218 

 influence of microbes on, 249 

 Reduction of nitrate, 145-152 

 Reduction processes of microbes, 249- 



250 

 Rhizodonia, 41 

 Rhizopus, 30, 33 



Rocks, disintegration of, by microbes, 

 180 

 weathering of, 2-6 

 Root excretions, 192-194 

 Roots, effects of microbes on, 201-202 

 influence of, on carbon dioxide 



production, 161 

 solvent action of, as influenced by 

 microorganisms, 188 



S 

 Saprophytic nature of microbes, 22, 



45 

 Season of year, influence of, on 

 microbial development, 64- 

 65 

 Soil, as a medium for development of 

 microbes, 19 

 atmosphere, 159 



chemical composition of, 3, 5, 6-8 

 conditions, influence of, on mi- 

 crobes, 87, 248 

 upon distribution of bacteria, 

 58-60 



