Meristematic Tissues Meristems are places in plants where cell division is

occurring.

During cell division, one cell becomes two cells. Each new cell can also divide.

Meristematic Tissues In this class we will discuss three kinds of meristems:

Apical Meristems

Intercalary Meristems

Lateral Meristems

Apical Meristems In plants belonging to

the DICOT class, apical meristems are located in BOTH the shoot tips and root tips. A shoot is simply a young, leaf-bearing stem.

In plants belonging to the MONOCOT class, apical meristems are located ONLY in the root tips.

Microscopic View of an Apical Meristem

Apical Meristems•Primary growth of shoots and roots occurs as the cells of the apical meristem divide and elongate.

Intercalary Meristems In addition to the apical meristems located in their

root tips, plants in the MONOCOT class have special meristems called intercalary meristems.

Intercalary meristems are located on monocots where the leaf bases connect to the stem of the plant.

Intercalary Meristems

Monocots, like grasses, have intercalary meristems which allow the leaves to grow back after mowing.

Lateral Meristems In addition to the

apical meristemslocated in the shoot and root tips, plants in the DICOT class have lateral meristems.

Lateral meristemscause SECONDARY GROWTH.

Secondary growth causes stems and roots to grow larger in diameter.

Lateral Meristems cause an increase in stem diameter

Lateral Meristems

Think of a lateral meristem as being a cylinder, several cell layers thick, of actively dividing cells.

Permanent TissuesPermanent tissues are of two types;

Simple permanent tissue

Complex permanent tissue

Simple permanent tissue Parenchyma

store food and water

Collenchyma provide support for plant organs

Sclerenchyma supporting function

secondary walls impregnated with lignin fibers and sclerids

may be nonliving at maturity

Parenchyma - are the general purpose ceIIs of plants - cells are

rounded in shape & have uniformly thin walls

found in all parts of the plants.

- living at maturity, have large vacuoles

- location Ieaf, stem (pith), roots, fruits

collenchyma cells are elongated (up to 2mm long) with unevenly

thickened walls ( thin on the sides but thick at the angles where 2 or more cells meet)

differentiate from parenchyma cells & are alive at maturity

sclerenchyma - sclerenchyma cells which are non-living and lack

protoplasts at maturityTypes:1. scIereids or stone cells2. fibers

Complex Permanent Tissues

Vascular Tissues- specialized for long-distance transport of water

and dissolved substances.

- contain transfer ceIIs, fibers in addition to parenchyma and conducting ceIIs

- location, the veins in Ieaves

types

1. Xylem

2. phloem

Xylem Xylem tissue conducts

water and dissolved mineral nutrients.

It is composed of columns of vessel cells (tracheids in gymnosperms), stacked one upon another, and fibers.

Vessel cell walls are pitted and allow water passage between the xylem and surrounding tissues. Mature xylem cells are dead.

Xylem Phloem

Xylary elements – the conducting cells in xylem

- 2 kinds of xylary elements:

tracheids – the only water conducting cells in most woody, non flowering plants.

vessel elements – occur in several groups of plants, including angiosperm.

- both are elongated, dead at maturity, lignified secondary cell walls

Phloem Phloem tissue conducts the

food produced by the leaves in a downwards direction to stems and roots (from source to sink).

Phloem is composed of sieve tubes, companion cells, and fibers.

The end walls of the sieve tubes are called sieve plates.

Xylem Phloem

Sieve tube elements – main conducting ceIIsof phloem

- elongated and non-nucleated

- uniformly thin walled with the end walls

perforated to from the sieve plate.

- sieve tube element are attached end to end to form the sieve tube.