. Principles of the anatomy and physiology of the vegetable cell. Plant cells and tissues. Porous cells of the leaf of Dicra- imm glauomn. come converted into porous cells. This occurs most remarkably in certain Mosses, especially in the fibrous cells of Sphagnum, the leaf-cells of Dioranwu glaucum (%.24), and OdoblepharuTn albidum, &c. (See "Anatomical researches on the Porous Cells of Sphagnum" in •my^VermischteSchriften/' 294; also Schleiden, "Beitrage/'L7l.) This phe- nomenon is very rare in the Phanero- gamia; I found it decidedly in fibrous- cells, , in the rind of
. Principles of the anatomy and physiology of the vegetable cell. Plant cells and tissues. Porous cells of the leaf of Dicra- imm glauomn. come converted into porous cells. This occurs most remarkably in certain Mosses, especially in the fibrous cells of Sphagnum, the leaf-cells of Dioranwu glaucum (%.24), and OdoblepharuTn albidum, &c. (See "Anatomical researches on the Porous Cells of Sphagnum" in •my^VermischteSchriften/' 294; also Schleiden, "Beitrage/'L7l.) This phe- nomenon is very rare in the Phanero- gamia; I found it decidedly in fibrous- cells, , in the rind of the root of Epidendrum elongatum, in the seed- coat of Martynia, fee, &c. Whether it occurs normally in the wood-cells of Pinus, as linger asserts, is yet a matter of doubt to me. In the generality of cases, all the layers deposited on the inside of the primary membrane agree completely in their form, so that there is no reason why we should adopt a further division of the layers than that into primary and secondary membrane. But in particular cases, the secondary membrane consists of two layers of strikingly difierent structure, so that it becomes necessary to dis- tinguish between primary, secondary, and tertiary membranes. To what extent such a distinction into secondary and tertiary membrane exists, cannot be stated in the present state of our knowledge. I must, therefore, confine myself to the mention of certain examples in which the existence of the tertiary membrane may be demonstrated with certainty. To these belong the wood cells of Taxus and Torreya, the primary and seconda^ mem- bx-anes of which are formed exactly as in the wood-cells of Pinus, but their cavity is lined with an inner membrane, which is covered with a fibre-like thickening running in regular spiral lines (fig. 25). The same structure is repeated in the wood- cells of certain Dicotyledonous trees, , in Viburnum Lantana, The contrast between the secondary and ter- tiary membranes is most stri
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