Page:Encyclopædia Britannica, Ninth Edition, v. 4.djvu/172

162 BOTANY from the spore of the asexual generation, or a small pro- embryo is first formed. The sporoffonium is of various forms, and originates differently in different groups from the oospore. It is always formed within a cellular covering or epigone. In Anthoceros the sporogonia are elongated and open by two valves, and there is a central cellular columella. In Jungermannia the sporogonia are globular, and open by four spreading valves. There is no central column, but the inner wall displays cellules, called elatcrs, fixed by one extremity, and containing one or two spiral fibres which by their elasticity scatter the spores. In Eiccia the sporogonia are globular, and there are neither elaters nor columella. InFuugi. Very little is known of the sexual reproduction of Fungi, and regarding the alternation of sexual and asexual generations in them. But we have abundant instances of alternation amongst the asexual generations, and along with this of that curious phenomenon included under the term hetercecism, which consists in the growth of one generation of a parasitic Fungus upon one host, and the development of another generation upon a different host. By tracing out this phenomenon, many forms, de scribed formerly as distinct species, are now shown to be generations of one and the same Fungus. The asexual spores of Fungi are produced upon certain structures which have been frequently termed the fructification. For in stance, in basidiosporous Fungi the collection of basidia forming the hymenium is usually situated on large re ceptacles. The structure commonly known as a fungus (tig. 356) is a receptacle produced upon a mycelium (my). In its young state it appears as a tubercle upon the mycelium covered by a volva (fig. 356, vol), or wrapper, which it bursts during growth. It consists of a pileus or cap (p), at the extremity of a stalk, the stipe (st). On the under surface of the pileus are the lamcllce (la) or gills, of various forms, which constitute the hymenial (Jiy) layer, to which the spores are attached. At first the hymenium is covered by a veil or indnsium, which during 357. The Truffle (Tuber cibarium), a subterranean Fungus, with a black tuberculated or w.-irty external covering, and a white cellular interior containing sporif erous cells. the growth of the stipe is ruptured, the base remaining on the stipe as the annulus (an) or ring. When, as in the Mushroom, the hymenium is exposed, the fungus is said to be gymnocarpous (fig. 356). In other cases, as in Phalloidese, it is covered over by a peridium, and the whole mass so enclosed is the f/leba, and the fungus is angiocarpous (fig. 357). In .ascosporous Fungi, as Spheeria, the asci are usually formed within small roundish receptacles, termed perithecia; and along with the asci are usually numerous abortive fila ments or paraphyses. Sometimes these perithecia are situated upon cushions or branching masses of tissue, the stroma. In the myxo- sporous Fungi the plasmodium, or whole protoplasmic mass of the plant, forms receptacles, in each of which is a cajnllitium, or network of fine filaments, in the interstices of which are numerous spores. In Lichens spores are formed in asci, which are ar- In Lichei ranged along with paraphyses, forming a hymenium in receptacles situated on the thallus, and termed apothecia or lirellce, which are sometimes (fig. 95) supported on a stalk or podetium. The hypha?, from which the asci arise, form a layer immediately beneath the hymenium, termed the sid)hymenial layer, the thick mass of hyphse beneath being the hypothedum. The outermost layer of the tissue of the apothecium is termed the excipulum. Amongst Algai alternation of generations is very com- In Algze. mon ; and here, as in the case of Fungi, it may pass through several generations before reaching the original form. This is well seen in Diatoms, also in CEdogonicai, where three generations are passed through, and in Coleo- cluete, where there are four dissimilar generations, sexual and various forms of asexual reproduction alter nating. (.1. II. B.) INDEX OF PRINCIPAL SUBJECTS. Absorption, 119. Chlorophyll, 87. Fibro-vascularbundles,92. Macrosporcs, 161. Pits, SO. Species,definilions of, 81. Achamium, 161. Circulation, 84. Filament, 130. Male organs of plants, Placenta, 142. Spcrmagones, 159. Acotyledonous plants, 92. Cone, 122, 153. Flowers, different parts 135-141. Pleurcnchyma, 85. Spcrmatozoids, 140. Acotyledons, stem in, 105; Conjugation, 159. of, 126. Medullary sheath, 100; Pod, 151. Spennodenn, 153. leaves in, 115. Connective, 137. Flower-bud, 130. rays, 102. Pollen, 138. Spike, 122. Acrogenous stem, 99. Corm, 98. Foliage leaves, 110. Micropyle, 154. Pollination, 139. Spikelets, 134. Aerial roots, 94. Corolla, 132. Follicle, 151. Microspores, 141, 161. Pome, 152. Spines, 97. Estivation, 130. Corpuscles, 146. Formula;, floral, 129. Monocotyledonous p ants, Prickles, 90. Spiral tissues, 8.5. Albumen, 155. Corymb, 122. Fovilla. 139. 92, 157. Primary tissue, 92. Sporangia, 1(, 0. , Algce, vegetative organs Cotyledons, 156. Fruit, 148-153. Monocotyledons, stem in, Protective organs of Stamens, 135. of, 107 ; reproduction Cremocarp, 151. Fungi, vegetative organs 103; leaves in, 115. flower, 131. Staminodia, 138. of, 162. Cryptogamous plants, 92. of, 107 ; reproduction Mosses, stem in, 100; Prothallus, 140. Starch, 88. Alternation of genera Cryptogams, male organs of, 162. female organs in, 158; Protoplasm, 84. Stem, 95-107 tions, 159. in, 140; female organs Glands, 91. alternation of genera Pulvinus, 113. Stigma, 144. Amentum,-122. in, 157. Globule, 140. tions in, 161. Putamen, 151. Stipe, 105. Anther, 136. Cyme, 123. Glumes, 119, 134. Natural classifications, SO. Raceme, 122. Stipules, 109, 111. Antheridia, 140. Dehisccnce, antherine, Gum, 88. Nectaries, 134. Raphe, 147. Stolon, 97. Archegonia, 157. 137. Gynoecium, 141. Nucleus, 84. Itaphides, 89. Stomata, 89. Arillus, 154. Dehiscence of fruits, 149. Hairs, 90. Nucule, 158. .Receptacle, 121. Strobilus, 122, 103. Asexual reproduction, Dicotyledonous plant s, 92, Herbaceous plants, 95. Nut, 151. Reproduction, organs of, Style, 144. 159. 156. Ilcsperidium, 152. Nutrition, organs of, 94- 119-162. Suckers, 97 Bark, ICO. Dicotyledons, stem in, 99 : Heteroecism, 162. 119. Resins, 88. Sugar, 88. Berry, 151. leaves in, 115. History of botany, 79. Oils, 88. Respiration, 119. Syconus, 153. Bordered pits, 86. Dictyogens, 105. Horsetails, stem in, 10G; Ovary, 143. Rhizocarps, stem in, 107; Symmetry of flower, 127 Bracts, 119. Disk, 139. reproduction of, 160. Ovule, 145. reproduction of, 161. legmen, 153. Branches, 97. Drupe, 151. Inflorescence, 121; tabular Panicle, 122. Khizome, 98. Tendrils, 97, 114. Branching, provision for, Kmbryo, 155. view of, 125. Pappus, 131. Uoot, 94. Testa, 153. 92. Embryo-sac, 146. Integuments, 89. Paraphyses, 160, Root-stock, 98 Thalamus, 121. Bulb, 99. Endogenous stem, 99. Intercellular spaces, 87. Parenchyma, 85. Rotation, 84. Thallogens, 95 ; stem and Calyx, 131. Envelopes of flower, 131. .lussieu, 80. Peduncle, 121. U tinner, 97. leaf of, 107; female Cambium, 99, 101. Epidermis, 89. /iticifcrotis vessels, 87. Pepo, 152. Samara, 151. organs in, 158. Caoutchouc, 83. Epiphytes, 94. .eaf-lnuls, 95. Petals, 132. Scales, 90, 115. Tissues, 83-87; of leaves, Capitulum, 123. Essential organs of flower, .caves, 103-119. Petioles, 109, 112. Seed, 153-157. 108. Capsule, 152. 134. -egume, 151. Phanerogamous plants,92. Sepals, 131. Transpiration, 119. Cm-pels, 141. Exhalation, 110. ^ichens, vegetative or Phanerogams, male or Septum, 142. Ti ichomes, 90. Caryopsis, 151. Exogenous stem, 99. gans of, 107 ; reproduc gans in, 135. Sexes of plants, 82, 134. Tuber, 98. Cells, 83. fall of leaf 119. tion of, 162. Phyllodium, 113. Sheath, 114. Umbel, 123. Cellular plants, 92. Fascicle, 124. Linnams s system of clas Phyllotaxis, 115. Siliqua, 152. Vascular plants, 92, Chalaza, 146. Female organs of plants, sification, 80. Physiology of plants, 81. Soboles, 98. Venation, 109. Characeae, stem 5n, 105, 141-1 59. I.oculaments, 143. Pistil, 141. Sori, 160. Vernation, 118. male organs in, 140; Ferns, stem in, IOC,, re Lycopodlaceas, stem in, 1 istillidia, 157. Sorosus, 153. Verticillasters, 124. female organs in, production of, 1GO. 107; reproduction of, Pitchers, il5. Spadix, 122. Wax, 88. 157. Fertilization, 147. 161. Pith, 100. Spatha, 120.

Wood, 100.