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From the primary vein, secondary and tertiary veins branch out, [3] forming a network that distributes resources throughout the leaf. The arrangement of veins, including the primary vein, varies among plants. Reticulate venation occurs in dicots, [4] where the primary vein branches into a network; parallel venation is found in monocots, where ...
Cross section of celery stalk, showing vascular bundles, which include both phloem and xylem Detail of the vasculature of a bramble leaf Translocation in vascular plants. Vascular tissue is a complex conducting tissue, formed of more than one cell type, found in vascular plants. The primary components of vascular tissue are the xylem and phloem ...
It forms a protective covering on the leaf vein and consists of one or more cell layers, usually parenchyma. Loosely-arranged mesophyll cells lie between the bundle sheath and the leaf surface. The Calvin cycle is confined to the chloroplasts of these bundle sheath cells in C 4 plants. C 2 plants also use a variation of this structure. [1]
In parallel veined leaves, the primary veins run parallel and equidistant to each other for most of the length of the leaf and then converge or fuse (anastomose) towards the apex. Usually, many smaller minor veins interconnect these primary veins but may terminate with very fine vein endings in the mesophyll.
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.
The movement of water out of the leaf stomata sets up transpiration pull or tension in the water column in the xylem vessels or tracheids. The pull is the result of water surface tension within the cell walls of the mesophyll cells, from the surfaces of which evaporation takes place when the stomata are open.
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Acrodromous – the veins run parallel to the leaf edge and fuse at the leaf tip. Actinodromous – the main veins of a leaf radiate from the tip of the petiole. Brochidodromous – the veins turn away from the leaf edge to join the next higher vein. Campylodromous – secondary veins diverge at the base of the lamina and rejoin at the tip ...