exsist at each stem tip

present in the embryo

-during germination, embryos plumule develops into stem

development of stem

terminal bud

-shoot apical meristem

-covered in protective leaves (bud scales)

stem development

axillary buds

-(lateral bud or primordium)

-also shoot apical meristems

-formed between leaf and stem

-may become branches or flowers

development of stems

primary apical meristem cells

protoderm

procambium

ground meristem

roots have pericycle for later growth

shoots leave behind buds 

stem development

leaf gap or scar

-vascular tissue goes off from cylinder of xylem and phloem and goes into leaf or bud 

-parenchyma tissue scar

each trace (strand of xylem & phloem) leaves gap filled with parenchyma tissue

vascular cambium

cork cambium

secondary growth

lateral growth 

secondary xylem towards center

secondary phloem towards outside of stem

lateral meristem

vascular cambium

secondary phloem

lateral meristem

vascular cambium

secondary xylem

lateral meristem

cork cambium

-arises from cortex

-produces cork cells w/ suberin towards outside

-and sometimes phelloderm towards inside (cortex)

-prevent water loss and protect stem

-lenticles: parenchyma cells in cork for gas exchange

lateral

cork cambium

phelloderm

-second layer of cortex

-food storage

-towards inside of stem between cortex and cork cambium

-solid core

-phloem surrounds xylem

-in dicot roots

-in many extinct seed plants and whisk terms and club mosses

-discrete vascular bundles

-in flowering plants, conifers stems, and monocot roots

1. herbaceous monocot stems

2. herbaceous dicot stems

3. woody dicot stems

-have neither vascular cambium or cork cambium

-primary xylem & phloem in discrete vascular bundles scattered

-xylem towards inside 

-herbaceous monocot stem:

tend to form layers of sclerenchyma or collenchyma beneath epidermis to give the plant rigidity

-no discrete pith & cortex

monocot stem

anomalous secondary growth

monocot stem

primary gigantism

continued division and enlargement of parenchyma cells

-palm trees

-vascular cambium makes parenchyma to the outside

-parenchyma and vascular bundles to inside

- this is secondary growth

herbaceous dicot stems

annuals 

- plants that die after maturity within one growing season

-green, herbaceous plants

-most monocots are annuals

-tissues largely primary

herbaceous dicot stems

-discrete VB in cylinder

-VB separate cortex from the pith

-VB grow so close

-vascular cambium arises between primary x & p, adding secondary x & p

-wood= secondary xylem

1) vascular cambium and cork cambium are active all year:

-no rings in wood

-tropical trees

2) active seasonally:

-spring: large VE and 2nd xylem produced-- Spring wood

-after spring wood: fewer and smaller VE compared to tracheas and fibers-- Summer wood

older darker wood in center

non conducting

-can be removed without affecting trees health

hardwood

wood of dicot trees

prolific VE lend structural stability to wood

-underground stems

-spreading or asexual reproduction

horizontal stems grow above ground

have long internodes

asexual reproduction

beneath surface 

grow in different directions

tubers formed when several internodes at tips of stolon enlarge together

-they store food

bulbs 

large buds 

specialized lead

-resemble bulbs

-composed almost entirely of stem tissue

prickles: modified epidermal tissue

spines: modified leaves

stems modified to assist epiphytic or climbing plants