Fig. 9.3-4. Magnification of ducts in wormwood. There are two ducts here, the one on the left is old enough to have developed a small lumen and epithelium; the one on the right has not yet reached the stage of having a lumen. The arrow points to an area where the cells might be starting to pull apart – the black material between the cells might be the first stages of the breakdown of the middle lamella (there are places in the upper part of this micrograph where there are similar amounts of dark material between cells, but those are the thickened corners of collenchyma cells). These young ducts occurred in the same histological section as older ducts, indicating that duct development is not completely simultaneous: it is fairly common in many species for ducts to be initiated at slightly different times or for some to mature more rapidly than others. However, it is somewhat unusual for a new duct to be initiated in a portion of stem, leaf or root that is so old it has completely mature, fully differentiated ducts already.