. Botany of the living plant. Botany. THE TISSUES OF THE STEM 41 position ; but additional sieve-tubes are present also on the side adjoining the pith. Cambial activity is evident between xylem and the outer phloem, and a few divisions are also seen between the xylem and the medullary phloem. The stems of climbing plants, and especially of the Cucumber and Vine, have been habitually used to demonstrate the structure of sieve-tubes J because there they are specially large. In Fig. 25 the. Fig 25. Transverse section of a vascular strand of the Cucumber, showing plentiful phloem both on periphera
. Botany of the living plant. Botany. THE TISSUES OF THE STEM 41 position ; but additional sieve-tubes are present also on the side adjoining the pith. Cambial activity is evident between xylem and the outer phloem, and a few divisions are also seen between the xylem and the medullary phloem. The stems of climbing plants, and especially of the Cucumber and Vine, have been habitually used to demonstrate the structure of sieve-tubes J because there they are specially large. In Fig. 25 the. Fig 25. Transverse section of a vascular strand of the Cucumber, showing plentiful phloem both on peripheral and central sides of the xylem (bicoUateral). The vessels of the xylem are few, but very large. sf=sieve-tubes, ^.r. = pitted vessels. ^;»;=protoxylem. ic'= interfascicular cambium. { x 75). sieve-tubes appear nearly circular in transverse section ; they are limited by a cellulose wall, and a cytoplasmic lining invests the wall during life. This readily contracts from the wall when the tissues are cut across, and the internal pressure relieved. That is the state in which they are usually observed. Associated with each is a small companion-cell, often triangular in transverse section, and with dense nucleated cytoplasm. Where a sieve-plate is included in the section it will present a surface perforated by dot-like pores. The contents are densely aggregated round the plate. Under a high power, when. 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 Bower, F. O. (Frederick Orpen), 1855-1948. London, Macmillan
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Keywords: ., bookcentury1900, bookdecade1910, booksubjectbotany, bookyear1919
