Introduction to Stems and External Features
· Stem is the axis of the plant other than the root
· In most plants stems are located above the soil surface but some plants have underground stems
· Functions of the stem
§ Stems support the leaves and other structures e.g. flowers, fruits
§ Stems are used for vegetative reproductive i.e. cuttings
§ Stems position leaves to receive maximum sunlight
§ Stems determine size and shape of the plant
§ Facilitates movement of water, minerals, and manufactured food in the plant
§ Some stems carry out photosynthesis
§ Stores foods
· External features of the stem
· External structures of the stem
§ Internodes: distances separating one node from another
§ Nodes: Points at which leaves are attached
§ Lenticels: Breathing pores
§ Buds:Growth of shoot
§ Terminal or apical but, at tip of plant
§ Axillary bud in nodes on stem
§ Bud scale scars: Indicate where terminal bud has been located previous year
§ Leaf scars:
§ Show where leaf was attached
· Internal structures of the stem
§ Usually consist of three tissues, Dermal tissue, Ground tissue and Vascular tissue
§ The dermal tissue
§ Covers outer surface of stem and usually functions to waterproof, protect & control gas exchange
§ The Ground tissue
§ Mainly of parenchyma cells and fills in around the vascular tissue, sometimes functions in photosynthesis
§ The Vascular tissue
§ Provides long distance transport and structural support
§ Arrangement varies widely among plant species
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