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Internal phloem is mostly primary, and begins differentiation later than the external phloem and protoxylem, though it is not without exceptions. In some other families ( Amaranthaceae , Nyctaginaceae , Salvadoraceae ), the cambium also periodically forms inward strands or layers of phloem, embedded in the xylem: Such phloem strands are called ...
The first xylem to develop is called 'protoxylem'. In appearance, protoxylem is usually distinguished by narrower vessels formed of smaller cells. Some of these cells have walls that contain thickenings in the form of rings or helices. Functionally, protoxylem can extend: the cells can grow in size and develop while a stem or root is elongating.
Phloem loading is the process of loading carbon into the phloem for transport to different 'sinks' in a plant. Sinks include metabolism , growth, storage, and other processes or organs that need carbon solutes to persist.
A sugar source is any part of the plant that is producing or releasing sugar. During the plant's growth period, usually during the spring, storage organs such as the roots are sugar sources, and the plant's many growing areas are sugar sinks. After the growth period, when the meristems are dormant, the leaves are sources, and storage organs are ...
Primarily, phloem carries dissolved food substances throughout the plant. This conduction system is composed of sieve-tube member and companion cells, that are without secondary walls. The parent cells of the vascular cambium produce both xylem and phloem. This usually also includes fibers, parenchyma and ray cells.
Cross-section of a flax plant stem: 1. Pith 2. Protoxylem 3. Xylem I 4. Phloem I 5. Sclerenchyma 6. Cortex 7. Epidermis. In botany, a cortex is an outer layer of a stem or root in a vascular plant, lying below the epidermis but outside of the vascular bundles. [1]
Xylem and Phloem. A stem is one of two main structural axes of a vascular plant, the other being the root. It supports leaves, flowers and fruits, transports water and dissolved substances between the roots and the shoots in the xylem and phloem, engages in photosynthesis, stores nutrients, and produces new living tissue. [1]
An example of analysis of phloem through sieve elements was conducted in the study of Arabidopsis leaves. By studying the phloem of the leaves in vivo through laser microscopy and the usage of fluorescent markers (placed in both companion cells and sieve elements), the network of companion cells with the compact sieve tubes was highlighted. The ...