. Contributions from the Hull Botanical Laboratory. Plants. 1919] Ml LLER—CYCA S MEDIA 217 walls. Fig. 9 shows characteristics of the xylem in that region of the cylinder where protoxylem would be expected if there were any. All cells are uniformly thickened and, without exception, equipped with bordered pits, which is always a mark of secondary origin. In fig. 10 the same region is seen in radial section. Here the xylem element nearest the stem center, and even bordering on pro- tophloem of the normal cylinder, is pitted. This one drawing illustrates tracheids of the first cortical cylinder w
. Contributions from the Hull Botanical Laboratory. Plants. 1919] Ml LLER—CYCA S MEDIA 217 walls. Fig. 9 shows characteristics of the xylem in that region of the cylinder where protoxylem would be expected if there were any. All cells are uniformly thickened and, without exception, equipped with bordered pits, which is always a mark of secondary origin. In fig. 10 the same region is seen in radial section. Here the xylem element nearest the stem center, and even bordering on pro- tophloem of the normal cylinder, is pitted. This one drawing illustrates tracheids of the first cortical cylinder which are as nearly scalariform as could be found; they are as rare as spiral tracheids are in the nor- mal cylinder. By far the greater number of xylem elements in this centrip- etal region of the cylin- der are pitted in exactly the same fashion as ordinary secondary tra- cheids of the normal cylinder, and they must in turn be considered as of secondary origin. In fig. 8 it will be seen that the region between the normal cylinder and the first cortical one is composed of purely cortical cells. Also the region between the first cortical cylinder and the split in the cortex, which marks the place where the second. Fig. 8.—Cycas media: transverse section of stem, showing entire second cylinder as it appears near tip of stem; ph', protophloem of first cylinder crushed; ph", secondary phloem of first cylinder; c, cortical cells; x", secondary xylem of second cylinder; /, unthickened xylem cells; cb, cambium; ph, secondary phloem of second cylinder; sp, split in cortex caused by expansion lower down of third cylinder; 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 Hull Botanical Laboratory. [Chicago : University of Chicago Press
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Keywords: ., bookcentury1800, bookdecade1890, booksubjectplants, bookyear1895
