Stems

STEMS

Professor Joan S. Awingan

Functions1. Support of main body of plant & leaves.

2. Conduct water & food.

3. It helps store water, as in cacti, and the products of photosynthesis, as in the trunk of sago palm (Metroxylon sagu) and sweet palm (Arenga pinnata) which store large stock of starch;

4. Young green stem also performs a minor role in the production of food through the process of photosynthesis, but in some species (e.g. cactus) the stem is the chief photosynthesizing organ.

5. The plant stem serves as a means of asexual reproduction in many plant species.

Parts of a Stem

A node is a point on the stem from which leaves or buds arise.

The portion between two successive nodes is the internode.

A bud is an embryonic stem which has the potential for further plant growth. It may develop into a leaf, flower, or both.

The first stem that develops from a seed arises from the epicotyl, an embryonic shoot within the seed.

CHARACTERISTICS OF HERBACEOUS STEMS

1. Has soft, green stem and naked bud2. Covered with epidermis3. Grow to a small diameter4. Lives only for one season (annual)5. With primary tissues only

CHARACTERISTICS OF WOODY STEMS

1. Has brown cover and chiefly covered by scales2. Covered with periderm or bark3. Grow to a considerable diameter4. Lives year after year (perennial)5. With secondary tissues

SECONDARY FUNCTIONS OF STEMS

1. Protection – with thorns (hard, straight, pointed structures; modified branches or stems)

Ex: Rose, Bougainvilla, citrus

2. Photosynthesis – young and green, helps in food productionEx: Kangkong, Squash

3. Unusual support – with tendrils (thin, leafless, spirally curvedor coiling structures at are sensitive to contact stimuli) attach the plant to the support

Ex: Squash, Ampalaya, Upo

4. Storage – succulent, can store either water or othermaterials Ex: mucilaginous substances – cactus, sabila

tannins – Acacia tree resin – coniferous trees latex – Rubber tree sugar - sugarcane

5. Reproduction – some plant stems can be used forvegetative reproduction such as grafting, marcoting,budding, layering, and marchingEx: underground stems like

runners – grasses tubers rhizomes

RHIZOMES - a horizontal underground stem, which grow near the surface of the soilEx: ginger

UNDERGROUND STEMS

TUBERS - enlarged ends of special underground branches.Each tuber has several eyes. Each eye can develop into anew plantEx: potato

BULBS - a short disk-shaped underground stem, with manyfleshy scale leaves.Ex: onion

CORM - short, stout, solid and more or less rounded in shape. It is filled with stored food and grows in a vertical direction.Ex: gabi

STEMS FOR ASEXUAL REPRODUCTION

RUNNER – a slender prostate branch with long or short internodes,creeping on the ground and rooting at the nodes; is sub-aerialEx: strawberry

STOLON – a slender lateral branch originating from an underground stem and growing horizontally outwards. It is likea runner, however, it is subterraneanEx: gabi, Bermuda grass

OFFSET – like runners, it originates in the axil of a leaf as a short,more or less thickened horizontal branch. It elongates only to acertain extent and produces at the apex a tuft of leaves and a cluster of small roots belowEx: water hyacinth

SUCKER – like the stolon, it is also a lateral branch developingfrom the underground part of the stem however, it growsobliquely upwards and directly gives rise to a leafy shoot ora new plant Ex: banana, bamboo

TENDRILS – thin, leafless, spirally curved branch by whichclimbers attach themselves to other objectsEx: upo, squash, ampalaya

OTHER SPECIALIZED STEMS

THORNS – a modified, hard, straight, sharp-pointed stem. It occurs in the axil of a leaf where a branch would normally develop.  Ex: lemon, roses, pomelo

CLADOPHYLLS – flattened stems and leaf-like in appearance.It has in its center a node bearing very small scale-like leaves with axillary budsEx: asparagus

PHYLLOCLADE – flat, stout and fleshy stems that are modifiedFor water and food storage. Generally found in plants whose leavesare very small, may fall off early or modify into spines. Then they take over the functions of the leaves, particularly photosynthesisEx: cactus