Structure and Function of Stem

Rod on plants have shape and size are very diverse. There branched stems and some are not branched. There is a rod that is small and some are very large in size, such as the type of Giant Sequoia trees. This tree has a height of 85 meters with an estimated age of about 2200 to 2700 years. This tree is considered to be the largest tree in the world in terms of volume. The volume of this tree in 2002 amounted to 1487 cubic meters. Sherman tree with Giant Sequoia type, located in Sequoia National Park in Visalia, California.

Stem usually serves to support the parts of a plant that is above ground, uphold and strengthen the plant body, with ramifications extending the field of photosynthesis, road transport water and minerals from ground, and the results of photosynthesis can be distributed to all parts of the plant until to roots. In addition, as a place to store food reserves. For example, the sugar cane plant, cactus, and potatoes. Stem can also serve as a breeding tool such as cassava stems, ginger, and mango crops.

A. MORPHOLOGICAL STRUCTURE OF STEM

Stem generally cylindrical shape or form, usually jointed and limited by the book, and the book leaves there. In plants dicot, stem form branching, while the monocot plants, stems not form branching. Morphologically, stem consists of :

a. books, which were attached leaves;
b. section, the area between the two books;
c. axillary buds (lateral) branches potentially forming buds;
d. terminal bud (tip / apical), the active part of growing and developing to make stem becomes higher.

Woody plants have hard, thick, and long lived stem. In the younger woody plant, there is chlorophyll so it can run the photosynthesis. In the older woody plant, cork layer is formed so the photosynthesis ability is disappeared. On the certain parts, there are small holes called lenticels. The stem of herbaceous plants is, such as water henna, quite soft since the absence of wooden tissue. Generally, the dicot stem is branched, while the monocot stem is not.

B. STEM ANATOMY STRUCTURE

Tissue arrangement on the stem are: epidermis, cortex and central cylindrical. The epidermis is composed of epidermal cells are covered with a fatty substance called kutin. Kutin form a protective layer called the cuticle. The epidermis is generally found in young stem dicot plants and stem monocot plants. In dikotil plants that are old, usually the epidermis has been damaged and replaced with bark. The cortex is composed of simple tissue, especially the parenchymal tissue. Limit cortex epidermis with cylindrical center. Some of the cells that make up the cortex may contain chloroplasts.



Cylindrical center or stele is the deepest part of the stem. The outermost layer of the stele is pericycle. In the pericycle there are pith parenchyma and vascular bundles. Cylindrical center consisting of xylem, phloem, cambium and pith. The composition of xylem and phloem varies in different plant species. In dicot plants and conifers, xylem and phloem cluster in a beam that surrounds the pith. At each beam vascular, phloem arranged on the outside and xylem on the inside. Among the xylem and phloem are vascular cambium. In monocot plants, xylem and phloem beam spread evenly on  simple tissue.

In plants dicot, tube bundle arranged in a circle, so that the cortex located on the outside of the circle and the pith on the inside of the circle. In this dicot plants, xylem arranged on the inside of the circle. Between the phloem and xylem, there are cambium causing secondary growth, ie growth that causes enlarged stem diameter. This growth will continue until it reaches the size of a giant. Lateral meristem activity is influenced by the seasons and the circle grows.

Cambium is a lateral meristem tissues that function in secondary growth. Two kinds of cambium which produce secondary plant tissue dicot, namely:
a. vascular cambium, the cambium that produces secondary xylem (wood) to the inside and secondary phloem to the outside,
b. cork cambium, the cambium which produces a hard and thick cover that replaces the epidermis in stems and roots.

Stem pith composed of parenchyma tissue that may contain chloroplasts. Pith has a real intercellular space consisting of a pericambium called pericycle. Pericambium limited by primary phloem in the inner and the endodermis in the outer. pith radius form of ribbons radier consisting of a row of cells, from the pith to the phloem. Its main function is hold the transport of food to the radial direction. In plants dicot, core radius appears in the form of fine lines that form a years circle.

C. FUNCTION OF STEM

Another stem funtion is the place where the leaves stick to; transpiration and gaseous excahange through the lentisel take place, and direct the leaves to the source of light. The vascular bundle inside the stem functions to provide the means of water and minerals and photosynthesis result transportation. Some stems of certain plants have particular function, for examples as the place to keep the food reserve of sago palm; as the place to keep the water of cactus; as the place where photosynthesis takes place of cactus; as  vegetative reproductive organs of cassava.