THE STEM. STRUCTURE & FUNCTIONS. General Terminology. Annual – a plant that completes its life cycle (seed, flower, fruit and seed) in one growing season. Ex. Crop plants Biennial – a plant that requires two growing seasons (2 years) to complete its life cycle. Ex. Asparagus
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STRUCTURE & FUNCTIONS
Vessels and tracheids
Seive tube elements and companion cells
As in roots, the activity of the vascular cambium in the stem gives rise to xylem towards the center and phloem towards outside. As new cells are added the diameter of the stem increases and the cortex and the epidermis are crushed and replaced.
Growth rings – growth layers which correspond to growing seasons.
Early wood – “spring wood”, abundance of rain and cooler temperature which allow cells to grow larger and more rapid.
Late wood – “summer wood”, less than optimal growing conditions, growth slows.
Sapwood – wood found between vascular cambium and heartwood, functions in the transport of water and solutes.
Heartwood – wood found in the center of the tree trunk, usually darker because of resins, oils and gums. Doesn’t transport water or solutes.