. Comparative anatomy of the vegetative organs of the phanerogams and ferns;. Plant anatomy; Ferns. INTRODUCTION; ig simplest cases Further divided by a tangential wall (e) into two cells, of which the outer is the initial of the dermatogen, the other of the periblem. The dermatogen remains in the simplest cases a simple layer, since its cells suffer only radial divisions alternately hori- zontal and vertical, but it may also be once more divided tangentially. The two other layers are further divided and developed by successive vertical walls in definite order, which need not now be followed;
. Comparative anatomy of the vegetative organs of the phanerogams and ferns;. Plant anatomy; Ferns. INTRODUCTION; ig simplest cases Further divided by a tangential wall (e) into two cells, of which the outer is the initial of the dermatogen, the other of the periblem. The dermatogen remains in the simplest cases a simple layer, since its cells suffer only radial divisions alternately hori- zontal and vertical, but it may also be once more divided tangentially. The two other layers are further divided and developed by successive vertical walls in definite order, which need not now be followed; later these are accompanied by transverse divisions into flats (Etagentheilung). In roots which increase much in thickness each outer cell, after the appearance of the wall c, may further divide by a radial vertical wall into two, in which the division by the wall e then takes FIG. 9.—Apex of the stem of Equisetum. A {330) loi^itudiiial section through a strong shopj of E. telmateja, B view of the apex of such a shoot from above ^Sachs); C, D, E, from E. arvense, after Cramer; C a diagrammatic' ground the apical cell and of the youngest segment, -D optical longitudinal section of the apex of a stem", E transverse section through I \n D, S in all cases the apical cell. The Roman figures 1, II,. , , {m B read IV for VI) indicate in a 1 cases the segments; the Arabic figures i, 9, 3 .. the successive division walls within a single segment; the letters iz, #,... in C and D the-successive principal walls. • In A, x,y indicate the highest, youngest rudiment of an annular swelling which will develope into a leafrSheal^; *5 the same older, bs apical cells of a still older leaf-rudiment, g rows of cells from which the vascular bundles are derived^z the .lowest layers of cells of the segments, r the rudiment of the cortex of the internodes ; the broad central band .between g and g the plerome. From Sachs'. Textbook. ' " ' . , , -. , In the apex of the stem o
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