11.1.2: Monocot Roots

Zea mays

Zea mays (corn) is often used as a model organism for monocot anatomy.

Figure \(\PageIndex{1}\): The images above show a corn seedling in two different stages of development. The first image is of the corn seedling at an earlier stage. It has produced a shoot (with one cotyledon) and a long root (radicle). In the second image, you can see that it has gotten larger by comparing the size of the seed coat from the corn kernel (caryopsis). The radicle has developed into a root system with many lateral roots branching off to the sides. Photos by Melissa Ha, CC BY-NC .

Figure \(\PageIndex{2}\): Corn root cross section. The major regions of the root are labeled in the cross section above. The epidermis is the outermost layer of cells and includes elongated cells called root hairs. The cortex is the region of cells between the epidermis and the vascular tissue. The pith is the region of cells contained within the cylinder of vascular tissue. A lateral root is emerging from the vascular cylinder. Photo by Maria Morrow, CC BY-NC.

Figure \(\PageIndex{3}\): Corn root cross section, close up of epidermis and root hairs. The epidermis is the outermost layer of cells, produced by the protoderm. These are parenchyma cells. The epidermis includes long, thin cells that project outward called root hairs. Root hairs are specialized for absorbing water and will only be found in young, growing root tips. The cells below the epidermis are part of the cortex. Many of these have become sclerenchyma cells with thick secondary walls. Compare the cell walls found in the epidermis to those found in the cortex. Photo by Maria Morrow, CC BY-NC.

Figure \(\PageIndex{4}\): Corn root cross section, close up of part of the vascular cylinder. A band of cells travels across the center of the image, making a slight arc. This is a segment of the vascular tissue, which is arranged in a cylinder within the root. The vascular cylinder is within a suberized layer of cells that forms the border of the cortex, called the endodermis. The suberin wax layer coating the endodermal cells is the Casparian strip. Just inside the endodermis (below it, in this image orientation) is a layer of cells called the pericycle. This is where lateral roots are produced. The phloem tissue is composed of pockets of cells with thinner walls (stained blue). The rest of the cells in the vascular cylinder have thick secondary walls (stained red) and are part of the xylem tissue. When the cells begin to have thin, blue-stained walls again (in this image), you've reached the pith. Photo by Maria Morrow, CC BY-NC.

Smilax

The organization of tissues in a Smilax root is similar to that in a corn root.

Figure \(\PageIndex{5}\): A cross section through a Smilax root. Compare this cross section to the corn root above. The staining is slightly different, so you cannot rely on color, alone. Image is in the Public Domain, sourced from Berkshire Community College Bioscience Image Library.

Figure \(\PageIndex{6}\): A close up on the multilayered Casparian strip of the Smilax root. The layers of Casparian strip look a bit like fingerprints or growth rings in wood, forming tightly packed layers surrounding each cell. Compare the thickness of this Casparian strip to the corn root. What would cause the difference in thickness? Image is in the Public Domain, sourced from Berkshire Community College Bioscience Image Library.