11.1.3: Eudicot Root Cross Section (Ranunculus)

Ranunculus

Figure \(\PageIndex{1}\): A cross section of a young Ranunculus root. The epidermis and cortex are in a similar arrangement as in monocots. However, the vascular cylinder has no internal pith region. Instead, it is composed entirely of vascular tissue with xylem at the center in a Y-shape and phloem filling the regions between the arms of the Y. Photo by Melissa Ha, CC BY-NC with labels added.

Figure \(\PageIndex{2}\): A close up on the cortex cells of the Ranunculus root. These cortex cells are also called storage cells because they contain many amyloplasts (stained purple) that store starch. Defined areas that do not contain amyloplasts are likely intercellular spaces (areas between cells). Photo by Maria Morrow, CC BY-NC.

Young Root

Figure \(\PageIndex{3}\): A close up on the vascular cylinder of the young Ranunculus root. At this stage, the vascular tissue does not have a well-defined boundary from the cortex (see the image on the left). Some of the xylem cells are stained red. These cells have developed their secondary walls and reached functional maturity. The others have only primary walls and are still developing. In the image on the right, the Y-shape of the xylem has been indicated by white lines. Those white lines represent the location of the procambium, which produces xylem to the inside and phloem to the outisde. One of the three pockets of phloem tissue is labeled. Photos by Maria Morrow, CC BY-NC.

Mature Root

Figure \(\PageIndex{4}\): A close up on the vascular cylinder of a mature Ranunculus root. The vascular cylinder is now clearly defined by the boundary of the endodermis (the innermost layer of the cortex), which is beginning to be covered by Casparian strip (which stains red, making the covered cells look like they have a secondary wall, but they do not). There are regions of the endodermis that appear to have no Casparian strip or only have it between adjacent cells. These groups of cells, called passage cells, are located at the tips of the four xylem arms (which are in an X-shape, now). Eventually, all of the cells in the endodermis will be coated. Photo by Maria Morrow, CC BY-NC.