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In dicots of the "Aristolochia" type, fascicular cambium is formed within each vascular bundle FROM REMNANTS OF PROCAMBIUM, which produces new, secondary xylem and phloem. To the inside bands of xylem are formed (one such band of secondary xylem is indicated in the figure as a purple overlay) that show growth rings (annual rings). The largest vessels are formed in spring, when the plant requires much water for growth. The vessels made during summer are much smaller. The secondary phloem is less extended. Amid the area's of secondary vascular tissue, interfascicular cambium generates broad rays of parenchymatic tissue. These rays form radial separations (septae) along the length of the stem and they connect pith and cortex together. Since the bands of xylem and phloem are intercalated with parenchyma tissue, the vine plant-like stem of Dutchman's pipe beholds some flexibility. In the cortex parenchyma cells differentiate to sclerenchyma (a type of supportive tissue). Parenchymatic cells laying a prolongation of the pith rays have undergone radial divisions. As a consequence the cortical region becomes filled up with cones of parenchymatic tissue, called dilation tissue, which separate the sclerenchymatic tissue into clusters (yellow arrows. See another example of dilatation tissue in linden).
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