. The natural history of plants, their forms, growth, reproduction, and distribution;. Botany. €26 THE SUBDIVISIONS OF THE VEGETABLE KINGDOM. exhibit a curious creeping movement, which is explained as being due to an external sheath or to filaments of protoplasm; the median line (or "raphe") shown by certain forms ( Navicula, fig. 369 *) is interpreted as a narrow slit at which this external protoplasm is extruded. Diatoms propagate by continuous longitudi- nal division; the valves are slightly separated, and division takes place parallel to the faces of the valves. Each daughter
. The natural history of plants, their forms, growth, reproduction, and distribution;. Botany. €26 THE SUBDIVISIONS OF THE VEGETABLE KINGDOM. exhibit a curious creeping movement, which is explained as being due to an external sheath or to filaments of protoplasm; the median line (or "raphe") shown by certain forms ( Navicula, fig. 369 *) is interpreted as a narrow slit at which this external protoplasm is extruded. Diatoms propagate by continuous longitudi- nal division; the valves are slightly separated, and division takes place parallel to the faces of the valves. Each daughter-cell thus possesses one of the valves of the mother-cell, and they complete their integument by secreting another on the side away from it. The new valve is always slightly smaller than the other one and. Kg. 369.—Diatoms, • Several Individuals of Synedra Ulna attached to a cell of an aquatic plant. 2 A single individual of Synedra Uh\a more highly magnified. » and < Navieula, Liber, seen from the side and from in front. = and « Similar views of Ifavieula tumida. ^ TriceratiuTn Favus. 8 Ccumpylodistms spiralis. ^ PleurosigTna angulatv/m. 10 and 11 GrammatopJwra ser- pentina. 12 and 18 Two views of Gomphonema capitatwm. i* Gomphoiiema capUatum on branched stalks which are attached to some algal filament is Diatom vidgare; the cells hang together into a zigzag hand, i^ and 1? FragUlaria virescens, showing an individual from two aspects and a row of six joined together into a ribbon, is Cocconema Cistula. 19 Two individuals of Cocconerrui Cistula inclosed in a mucilaginous envelope preliminary to auxospore-formation. 20 xhe two auxospores have elongated, and the old cases are seen to right and left; there is no conjugation in this instance. All highly magnified. fits under its rim, so that the Diatoms arising in this way become smaller and smaller till a certain minimum is reached. When this diminution has gone on for a certain period an enlargement is attained by the
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Keywords: ., bookcentury1800, bookdecade1890, booksubjectbotany, bookyear1895
