Bacteria, association with algæ in nitrogen fixation, 111; anærobic respiration of, 37; effect of arsenic on, 61; cellulose destroying, 134; changes in morphology in culture, 22, 47; classification of main groups, 23, 25; composition of cells of, 39; inverse relationship with protozoa, 10, 79, 82 _sqq._; isolation from soil, 21; methods of describing, 21; method of estimating numbers of, 53 _sqq._, 80; nitrogen fixation by, 110, 111; numbers in relation to algæ, 110; numbers in soil, 52 _sqq._; oxidation of hydrogen by, 27, 37; effect of partial sterilisation on, 8, 9, 66, 67; part played in soil fertility by, 7; pure cultures, isolation by plating, 20; seasonal changes in numbers of, 59, 87 _sqq._; effect of salts on, 60; short time changes in numbers of, 11, 57, 58; effect of temperature on, 67; uneven distribution of, 57. _Basidiomycetes_, 119, 123, 132. Beets, attacked by _Phoma betæ_, 135. _Boletus_, 132. _Botrytis_, 122. Bryophyta, 100, 132. _Bumilleria_, 105. CALCIUM compounds in soil and fungi, 139. _Carabidæ_, 150. Carbohydrates, decomposition by bacteria, 26 _sqq._; decomposition by fungi, 140; decomposition in soil, 168; effect on ammonia production in soil, 33; presence in algal sheath and bacteria, 111. Carbon, changes in amount in soil, 167; relationships of bacteria, 27; relationships of fungi, 133; source of, for soil bacteria, 39; sources of, for soil fungi, 139. Carbon dioxide, assimilation by algæ, 99, 107, 108; assimilation by soil bacteria, 35, 36, 40. Carotin, in algæ, 100; formed by _Spirochæta cytophaga_, 29. _Cecidomyidæ_, 155. Cellulose, decomposition by bacteria, 27, _sqq._; decomposition by fungi, 133, 134, 141; relation of nitrogen supply to decomposition of, 30; decomposition in soil, 168; as source of energy for nitrogen fixation, 43. Centipedes, see _Chilopoda_. _Cephalosporium_, 120. _Cephalothecium_, 136. _Chilopoda_, 157. _Chironomidæ_, 155. _Chlorella_, 108. _Chlorococcum_, 105. _Chlorophyceæ_, 100. Chlorophyll, loss of, from algæ, 108. Ciliates, classification of, 72; cyst wall of, 73. Citric acid, formation of, by fungi, 139. _Cladosporium_, 119. Clamp connections in fungi, 119. Classification, of algæ, 100; of bacteria, 23, 25; of fungi, 131; of protozoa, 69 _sqq._ Climate, effect of, on algæ, 101. _Clostridium_, 41, 44; as fixer of nitrogen, 6. _Coccomyxa_, 104. _Coleoptera_, 150, 154, 155. _Collembola_, 150, 153, 154. _Colletotrichum_, 131. Commensals, 132. _Conjugatæ_, 100. _Cortinarius_, 132. Cotton, destroyed by fungi, 134. Counting, of algæ, 109; of bacteria, 53 _sqq._; of fungi, 122; of protozoa, 77, 79, 80. Cresol, decomposition of, by bacteria, 22, 24, 31. Criteria, physiological, of fungi, 128. Crop growth, effect on fungi, 122. _Cryptomonadineæ_, 100. Cucumber leaf spot, 131.