Monocot vs. Dicot Angiosperms are divided into monocots and dicots As the zygote grows into the embryo, the first leaves of the young plant develop and are called cotyledons (seed leaves) Monocots have one cotyledon (corn, lily, etc). Dicots have two cotyledons (bean, oak, etc).

FEATURE MONOCOTS DICOTS Cotyledons 1 2 Leaf venation parallel broad Root system Fibrous Tap Number of floral parts In 3’s In 4’s or 5’s Vascular bundle position Scattered Arranged in a circle Woody or herbaceous Herbaceous Either

Life cycles From Outlaw’s lecture series

Angiosperm life cycle Floral structure Gametophytes Today From Outlaw’s lecture series

Monocot seed development typical monocot (maize) seed with ovary wall (pericarp) Monocots have one cotyledon (scutellum in grasses) that matures during germination Source of nutrition for seed germination: endosperm (compare to dicot) Maize fruit and seed

Dicot seed development dicot - two cotyledons mature immature Three tissue systems: Dermal Vascular Cortex or Ground All cells of the primary growth in dicots are part of these three systems and originate at meristems . . . A reminder that endosperm is formed in all angiosperms, but does not persist in dicots. In dicots, cotyledons are the primary source of nutrients for germination.

Seed germination What causes a seed to resume growth? What is growth? Broadly, where do the energy and basic elements required for growth come from? What observations did you make while germinating seeds? Plants-In-Motion Time-lapse videos of plant growth and response

Dicot germination and seedling An example of epigeous (epi=above, geo=earth) germination

Dicot germination and seedling An example of hypogeous (hypo=below, geo=earth) germination

Monocot germination and seedling

Root the first structure to emerge from the germinating seed Typical dicot Taproot persists and grows deep into the ground Typical monocot Taproot does not persist and adventitious roots originate from the shoot Notice the high surface volume: area ratio

Roots - Comparisons Fibrous roots: Taproots: Typical of dicots, primary root forms and small branch roots grow from it In monocots mostly, primary root dies, replaced by new roots from stem

Tap Root vs. Fibrous Root What are the functions of roots? From Outlaw lecture Typical of a dicot Typical of a monocot

Organization of the plant body Meristem = group of perpetually “embryonic” cells Apical = at the tip (of the root, the shoot, including laterals)

Diagram of major parts of primary dicot plant body Vascular tissue is throughout the plant body

Ground tissue of typical dicot root and shoot Buttercup (Ranunculus) Shoot Alfalfa (Medicago)

Vascular tissue of typical dicot root Buttercup (Ranunculus)

Dicot Root The Casparian strip is a layer of impermeable lignin and suberin that does not permit water and mineral ions to pass between adjacent cell walls. The only access to the vascular cylinder is through the endodermal cells themselves.

Monocot Roots

Secondary Growth (root) Example cross section of the dicot root in primary growth The cambium (perpetually meristematic layer between xylem and phloem) divides mitotically, producing either: A secondary xylem cell to the inside and a replacement cambial cell. OR A secondary phloem cell to the outside and a replacement cambial cell. Secondary growth rare in monocots From Outlaw’s lecture

Roots – Structure and Development Epidermis Primary phloem Primary xylem Pith Monocot Eudicot Endodermis Cortex Pericycle 48 µm 385 µm 8 µm Location of Casparian strip

Vascular tissue of typical dicot shoot Alfalfa (Medicago)

Herbaceous dicot stem

Monocot stem

Primary tissues differently organized in angiosperm shoots Typical of monocots Typical of dicots

Example dicot stem cross section Primary tissues differently organized in angiosperm shoots Example dicot stem cross section vascular bundles in ring with defined pith and cortex Shoot Alfalfa (Medicago)

Example monocot stem cross section Primary tissues differently organized in angiosperm shoots Example monocot stem cross section vascular bundles scattered Maize (Zea)

Secondary Growth (shoot) Example cross section of the dicot shoot in primary growth The cambium (perpetually meristematic layer between xylem and phloem) divides mitotically, producing either: A secondary xylem cell to the inside and a replacement cambial cell. OR A secondary phloem cell to the outside and a replacement cambial cell. From Outlaw’s lecture