Coal; its history and uses . Fig. 11. Selaginella. A, fertile branch (one-half natural size). B, apex inlongitudinal section, bearing microspores on the left, and macrosporeson the right (magnified). From Sachs Botany. English species (Lycopodium Selago) they are nearlyuniform with them, and the upper part of the spike,which bears sporangia, is in this species hardly distin-guishable in outward appearance from the rest. In ourother Lycopodiums the fertile leaves are clustered together COAL PLANTS. 101 into separate cones, whicli differ from the sterile branchesin shape and size (resembling thu
Coal; its history and uses . Fig. 11. Selaginella. A, fertile branch (one-half natural size). B, apex inlongitudinal section, bearing microspores on the left, and macrosporeson the right (magnified). From Sachs Botany. English species (Lycopodium Selago) they are nearlyuniform with them, and the upper part of the spike,which bears sporangia, is in this species hardly distin-guishable in outward appearance from the rest. In ourother Lycopodiums the fertile leaves are clustered together COAL PLANTS. 101 into separate cones, whicli differ from the sterile branchesin shape and size (resembling thus the fossil Lepidostro-bus), and also in colour. If one of these fertile Lycopo-dium cones be cut through vertically, the sporangia areseen nestling in the axils of the leaves, one at the base of. Pig. 12. Development of sporangia and spores of Selaginella, in order ofthe letters A—D. A, B serve for all the sporangia; c, D for micro-sporangia only. B, division of mother-cells of microspores ; A, fournearly ripe spores. (Magnified.) From Sachs Botany. each. The contents of a sporangium, originally a cellularmass, (fig. 12, a) arrange themselves gradually into anouter cellular wall and a cluster of inner cells, the mothercells. These give rise by division to spores, four to eachmother-cell. In Selaginella, a genus of Lycopodiaceseabundant in some tropical countries, but represented by a 102 COAL. CHAP. 111. single and not very common species in the British Islands,the spores are of two kinds, and the capsules in whichthey are lodged differ also when mature. In Lycopodiumbut one kind of spore appears to exist. Many of theCarboniferous club-mosses are of the Selaginella type,and we. shall therefore take this form for express com-parison. Selaginella, then, has sporangia of two ki
Size: 1497px × 1669px
Photo credit: © The Reading Room / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1800, bookdecade1870, bookpublisherlo, booksubjectcoal
