. A text-book of elementary botany. Botany. THE CELL AND TISSUE. 65 tion. This is called the circulation (Fig. 97) of the proto- plasm. In other cases it moves as a broad stream around the cell-wall. This movement is called the rotation (Fig. 98). 5. The cell wall often remains quite thin. In some of the bast-cells, in wood-cells and many others, it becomes very- thick ; but its growth in thickness is not uniform. Only a spiral band becomes thickened in very many cases; occasion- ally a thickened ring or annular band is formed. Sometimes the whole wall except small circular areas here and ther
. A text-book of elementary botany. Botany. THE CELL AND TISSUE. 65 tion. This is called the circulation (Fig. 97) of the proto- plasm. In other cases it moves as a broad stream around the cell-wall. This movement is called the rotation (Fig. 98). 5. The cell wall often remains quite thin. In some of the bast-cells, in wood-cells and many others, it becomes very- thick ; but its growth in thickness is not uniform. Only a spiral band becomes thickened in very many cases; occasion- ally a thickened ring or annular band is formed. Sometimes the whole wall except small circular areas here and there at- tains a considerable thickness. Simple pits in the wall result from such growth. Bordered pits are formed in the wood- cells of the Pine family. The sides of the pit arch over as growth in thickness proceeds—the upper margin thus making the inner ring, and the bottom of the pit the outer ring, when. pi. 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 Kellerman, William Ashbrook, 1850-1908. Philadelphia, Eldredge & Brother
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