Describe the structure and state the functions of stems.

State the primary functions of the stem - holding leaves and flowers in optimum positions and transport between roots and leaves

STEM

STEM FUNCTION

Primary function is to

hold leaves and flowers in optimum position and

provide a transport link between roots and leaves.

Also:

Protection (stem spines/thorns of Crataegus/prickles of Rosa) also used for climbing.

Storage or perennation:

Corms – Crocus, stem tubers – Begonia, rhizomes – Iris germanica.

Climbing:

Wisteria by twisting.

Natural vegetative reproduction:

Stolon’s or runners – Fragaria, rhizomes – Festuca rubra, stem tubers – Solanum tuberosum.

Describe the structure of the stem and state the functions of its components - internal structures to include drawing of a transverse section through a young dicotyledon stem to show the following components: epidermis, cortex, cambium, phloem, xylem, pith, vascular bundle and external structures to include lenticels, nodes, axillary and apical buds, scars (scale and leaf).

STEM STRUCTURE

PITH Pith (may be hollow) thin walled cells, with big intercellular air spaces: Store water and starch allows gaseous exchange.

STEM CORTEX Cortex – 3 layers of differing tissues: Outer cells have thickened walls providing strengthening of the stem – can contain chloroplast. Mid-cells are large with large air spaces – they store starch and allow gaseous exchange. Inner cells – the endodermis single layer of tightly packed cells which store starch and allow solutions to pass from the cortex to the vascular bundle.

LENTICEL See stem-features

NODE (STEM) See stem-features

INTERNODE See stem-features

APICAL BUD See stem-features

AXILLARY BUD See stem-features

GIRDLE SCAR See stem-features

BUD SCALE See stem-features

LEAF SCAR See stem-features

Describe how the stem is adapted to perform other functions - protection: stem spines (thorns of Crataegus) and prickles of Rosa; storage/perennation: corms (Crocus) stem tubers (Begonia) and rhizomes (Iris gemanica), climbing: (Wisteria passiflora); natural vegetative reproduction: stolons/runners (Fragaria), rhizomes (Festuca rubra), stem tubers (Solanum tuberosum).

SPINES (STEM) Protective funcrtion of stems.

THORN Protective funcrtion of stems.

PRICKLE Protective funcrtion of stems.

CORM Storage or perennation through stem eg Crocus

STEM TUBER Storage or perennation through stem tubers – Solanum tuberosum.

RHIZOME Storage or perennation through rhizomes – Festuca rubra

Stolon’s or runners Fragaria (strawberry)

see STOLON