Greek: angeion case; sperma seed

By far the most diverse group of plants that has ever existed with more than 240,000 different species.

The angiosperms

Why are there so many speciesOrigin of angiosperms Time scale

Mos

ses

Fer

ns

Angiosperms

Why are there so many species?

Gondwana

Gondwanaland

Angiosperms probably originated in the tropics

West Gondwana, equivalent to modern South America plus Africa

1. Leaves have finely divided venation

6. Generally hermaphrodite flowers and cross pollinating (70%)

4. Ovules protected within an enclosed structure

5. Double fertilization to produce diploid zygote and triploid endosperm nucleus

2. Xylem contains vessels as well as tracheids and parenchyma

3. Phloem contains sieve elements with companion cells

Principal differences between Gymnosperms and Angiosperms

ExamplesGrasses

Triticum, wheat

Zea mays corn

lillies

Oak trees, Quercus

Coleus

Lycopersicon, tomato

Potato, Solanum tuberosum

Monocotyledons and Dicotyledons

Typically veins are distributed such that mesophyll cells are close to is a vein.

The network of veins also provides a supportive framework for the leaf.

Angio-Gymno 1. Leaves have finely divided venation

Coleus leaf cleared of cell contents and with xylem stained A dicotyledon

Leaf of a monocotyledon plant

The major venation follows the long axis of the leaf and there are numerous joining cross veins so that, as with the dicotyledon, mesophyll cells are always close to a vein.

Diagram of a dicot leaf

Tomato leaf

Upper epidermis

Lower epidermis

Pallisade parenchyma: chloroplasts visible around cell periphery

Spongy parenchyma

Longitudinal section through a vascular bundle

Xylem vessel: annular thickening around cell wall

Phloem

Bundle Sheath

Ficus leaf

Lower epidermis

Pallisade parenchyma

Spongy parenchyma

Vascular bundle

Ficus, the fig, is a xerophyte

Collenchyma forming a hypodermis

Collenchyma above and below the vascular bundle

http://www.uri.edu/artsci/bio/plant_anatomy/99.html

Leaf cross section of Bouteloua

Bulliform cells

Bundle sheath cells with chloroplasts

Parenchyma with chloroplasts

Phloem

Xylem

Lower epidermis

Upper epidermis

Sclerified fibers

Collenchyma

… C3 and C4 photosynthesis?

http://www.uri.edu/artsci/bio/plant_anatomy/99.html

Leaf cross section of Zea mays ("corn").

Bulliform cells

Bundle sheath cells with chloroplasts

Parenchyma with chloroplasts Phloem

Xylem

Lower epidermis

Upper epidermis

Bundle sheath cells filled with chloroplasts. CALVIN REACTION SITE

Xylem

Phloem

Parenchyma filled with chloroplasts

C4 acids synthesized in the parenchyma move to the bundle sheath

Carbon skeleton compounds return to parenchyma

Anatomical separation of the C4 photosynthesis component processes

Angio-Gymno 2. Xylem contains vessels as well as tracheids and parenchyma

Angio-Gymno 3. Phloem contains sieve elements with companion cells

Ways in which Angiosperms are different from Gymnosperms

Angiosperm xylem and phloem

In Angiosperms Xylem and Phloem contain more specialized cells than in Gymnosperms as well as containing Fibers and Parenchyma.

Xylem: Vessel Elements

Phloem: Sieve elements, Companion cells

Vessels

Elongated vessel element: This cell provides moderate support and fluid conduction.

Vessel

Tracheid

Wide vessel element: This kind of cell is better for fluid conduction than physical support.

These vessel elements have completely perforated end walls

Tracheids provide better support but less slower rates of water conduction than vessels

A vessel is composed of several vessel elements

Tracheids lack perforation plates but their end walls contain numerous pits.

Phloem

STMs and CCs develop from the same progenitor cell. STMs, are columnar cells and unite vertically to form a Sieve Tube. STMs have no nucleus at maturity and depend on CC to regulate physiological processes. Each STM has one to several CC. The Sieve Plate is analogous to a Perforation Plate in vessels.

Sieve Tube Members (STM)

Sieve plate

Cucurbita phloem

Companion Cells (CC)

(cucumber)

Stems as diverse as slender vines, fat cacti, or as modified as potato tubers all have this organization, but with various zones modified. Cacti are so wide because they have an exceptionally thick cortex. Potato tubers have a gigantic pith and almost no wood.

Dicotyledon stem cross section

Angelica stem transverse section is typical of a dicotyledon plant without secondary thickening.

Four zones: 1) epidermis2) cortex, in many species the outermost part is a hypodermis3) ring of vascular tissues, usually a ring of vascular bundles4) pith.

J. D. Mauseth

We eat Angelica in confectionary

Transverse section of corn stem, Zea mays.

Transverse section of corn stem, Zea mays.

There are four parts:1) epidermis2) cortex with or without part differentiated into a hypodermis3) vascular bundles4) a matrix of parenchyma called conjunctive tissue or pith

This is the organization of monocot stems: numerous vascular bundles distributed throughout a tissue that may be either parenchyma or collenchyma

Vascular bundles

17.10, 31.2 through 31.6

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