A. STRUCTURE AND ORIGIN OF SOREDIA 141 _a._ Scattered soredia _b._ Isidial soredia _c._ Soredia as buds B. SORALIA 144 _a._ Form and occurrence of soralia _b._ Position of soraliferous lobes _c._ Deep-seated soralia C. DISPERSAL AND GERMINATION OF SOREDIA 147 D. EVOLUTION OF SOREDIA 148 4. ISIDIA A. FORM AND STRUCTURE OF ISIDIA 149 B. ORIGIN AND FUNCTION OF ISIDIA 151 VI. HYMENOLICHENS A. AFFINITY WITH OTHER PLANTS 152 B. STRUCTURE OF THALLUS 153 C. SPORIFEROUS TISSUES 154 CHAPTER IV REPRODUCTION I. REPRODUCTION BY ASCOSPORES A. HISTORICAL SURVEY 155 B. FORMS OF REPRODUCTIVE ORGANS 156 _a._ Apothecia _b._ Perithecia C. DEVELOPMENT OF REPRODUCTIVE ORGANS 159 1. DISCOLICHENS _a._ Carpogonia of gelatinous lichens _b._ Carpogonia of non-gelatinous lichens _c._ General summary _d._ Hypothecium and paraphyses _e._ Variations in apothecial development _aa._ Parmeliae _bb._ Pertusariae _cc._ Graphideae _dd._ Cladoniae 2. PYRENOLICHENS _a._ Development of the perithecium _b._ Formation of carpogonia D. APOGAMOUS REPRODUCTION 174 E. DISCUSSION OF LICHEN REPRODUCTION 177 _a._ The Trichogyne _b._ The Ascogonium F. FINAL STAGES OF APOTHECIAL DEVELOPMENT 181 _a._ Open or closed apothecia _b._ Emergence of ascocarp G. LICHEN ASCI AND SPORES 184 _a._ Historical _b._ Development of the ascus _c._ Development of the spores _d._ Spore germination _e._ Multinucleate spores _f._ Polaribilocular spores II. SECONDARY SPORES A. REPRODUCTION BY OIDIA 189 B. REPRODUCTION BY CONIDIA 190 _a._ Rare instances of conidial formation _b._ Comparison with Hyphomycetes C. CAMPYLIDIUM AND ORTHIDIUM 191 III. SPERMOGONIA OR PYCNIDIA A. HISTORICAL ACCOUNT OF SPERMOGONIA 192