Transverse section of a vascular bundle of a young stem of a buttercup (Ranunculus sp.)
This image shows details of a vascular bundle from a young stem of a buttercup (Ranunculus sp.), a dicot. The red cells at the bottom of the image are xylem vessels. The smaller vessels in the centre are known as protoxylem, and are those first formed when the stem is elongating. The larger outer cells are called metaxylem. These cells mature later, when the stem has finished elongating. During their development, the cellulose walls of vessels become impregnated with lignin. Lignification supports the vessels and prevents them collapsing under tension. During the process of lignification the cells die and form continuous non-living tubes that transport water and mineral ions from the roots.
Above the xylem is a region stained green, which contains the phloem. Phloem consists of sieve tubes, which transport the products of photosynthesis from the leaves, along with their associated companion cells. Sieve tubes are living cells, but they lack nuclei. Each sieve tube has cytoplasmic connections to a smaller companion cell that provides the energy requirements of the sieve tube.
Between the xylem and phloem are some very small, undifferentiated cells called the cambium.
Cambium within a vascular bundle is called fascicular cambium. The parenchyma cells between vascular bundles can also develop into interfascicular cambium. This results in a complete ring of cambium around the periphery of the stem, which can divide mitotically and differentiate to produce more xylem and phloem, during the process called secondary thickening.
The diameter of the image is about 150 µm.
Image by John Adds
Transverse section of a vascular bundle of a young stem of a buttercup (Ranunculus sp.)
This image shows details of a vascular bundle from a young stem of a buttercup (Ranunculus sp.), a dicot. The red cells at the bottom of the image are xylem vessels. The smaller vessels in the centre are known as protoxylem, and are those first formed when the stem is elongating. The larger outer cells are called metaxylem. These cells mature later, when the stem has finished elongating. During their development, the cellulose walls of vessels become impregnated with lignin. Lignification supports the vessels and prevents them collapsing under tension. During the process of lignification the cells die and form continuous non-living tubes that transport water and mineral ions from the roots.
Above the xylem is a region stained green, which contains the phloem. Phloem consists of sieve tubes, which transport the products of photosynthesis from the leaves, along with their associated companion cells. Sieve tubes are living cells, but they lack nuclei. Each sieve tube has cytoplasmic connections to a smaller companion cell that provides the energy requirements of the sieve tube.
Between the xylem and phloem are some very small, undifferentiated cells called the cambium.
Cambium within a vascular bundle is called fascicular cambium. The parenchyma cells between vascular bundles can also develop into interfascicular cambium. This results in a complete ring of cambium around the periphery of the stem, which can divide mitotically and differentiate to produce more xylem and phloem, during the process called secondary thickening.
The diameter of the image is about 150 µm.
Image by John Adds