. Elements of plant anatomy;. Botany -- Anatomy. 16 ELEMENTS OF PLANT ANATOMY. Centripetal growth is by far the more frequent and includes all growth in -thickness of walls common to two cells. It is found in cells of both classes, those where the thickening is uniform, and those where it is ir- regular. Of the former class, the ordinary bast and libriform cells furnish the best examples, where the primary wall is increased in thickness centripetally until only a small cavity remains. Of the latter class there are various kinds. Beginning with those where only a small portion is thickened, the
. Elements of plant anatomy;. Botany -- Anatomy. 16 ELEMENTS OF PLANT ANATOMY. Centripetal growth is by far the more frequent and includes all growth in -thickness of walls common to two cells. It is found in cells of both classes, those where the thickening is uniform, and those where it is ir- regular. Of the former class, the ordinary bast and libriform cells furnish the best examples, where the primary wall is increased in thickness centripetally until only a small cavity remains. Of the latter class there are various kinds. Beginning with those where only a small portion is thickened, the larger part re- maining thin, we have: I. Small circular spots of surface thick- A B ened, producing cone or rod-like projections which extend into the A piece of rhizoid of Marchantia poly- morpha. B epithel cells of petal of Pelargonium zonale. r projections into cell lumen, x 300. — (Wiesner.) Examples : Rhizoids of Marchantia and certain ducts whose walls are strengthened by conical inward projections. (See Fig. 9.) II. The thickening is not limited to spots but runs in continuous spirals with varying closeness of coil. Examples : Spiral ducts. III. Wall thickened in separate rings. Examples : Ring ducts. (Fig. 10.) IV. The thickened ridges run parallel to the long axis of growth and are con- nected by short cross-bars. Examples : Ladder, or scalariform Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Gregory, Emily L. Boston, London, Ginn & Co.
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Keywords: ., bookcentury1800, bookdecade1890, booksubjectbotanya, bookyear1895
