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Fanwort (Cabomba caroliniana). The aquarium plant fanwort demonstrates the great . The fanwort has feathery underwater leaves and large, flat, floating surface leaves. Both leaf types have genetically identical cells, but the dissimilar environments in which they develop cause different genes involved in leaf formation to be turned on or off

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Primary growth at the root and shoot apical meristems allow the plant to grow in length.

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The formation of a lateral root.
A lateral root originates in the pericycle, the outermost layer of the vascular cylinder of a root, and grows out through the cortex and epidermis.

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Primary tissues in young roots.

A dicot such as Ranunculus (buttercup) has a central core of xylem and phloem forming a vascular cylinder, or stele.

A monocot such as Zea (maize) has a vascular cylinder with a core of parenchyma cells surrounded by a ring of xylem and phloem.

Lateral roots originate from the vascular cylinder.

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Primary growth of a root.

Mitosis is concentrated in the zone of cell division, where the apical meristem is located.

The apical meristem also maintains the protective root cap by generating new cells that replace those that are sloughed off.

Most lengthening of the root is concentrated in the zone of elongation.

Root cells become functionally mature in the zone of maturation.

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Secondary growth occurs in the vascular cambium and cork cambium and adds girth to roots and stems.

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Organization of primary tissues in young stems.
(a)	A eudicot stem (sunflower), with vascular bundles forming a ring. Ground tissue toward the inside is called pith, and ground tissue toward the outside is called cortex.	(b)	A monocot stem (maize) with vascular bundles scattered throughout the ground tissue. In such an arrangement, ground tissue is not partitioned into pith and cortex.

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The terminal bud and primary growth of a shoot.

Leaf primordia arise from the flanks of the apical dome of a terminal bud, giving rise to a repetition of internodes and leaf-bearing nodes.

Lateral shoots arise from preexisting axillary buds on the surface of a stem.

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1. Apical meristem initiates primary growth.
2. Secondary xylem forms to the inside of the vascular cambium and secondary phloem to the outside.
3. Ray cells move water and nutrients between the secondary xylem and secondary phloem.
4. The cork cambium produces cork cells, which replace the epidermis.
5. In year 2, the vascular cambium adds to the secondary xylem and phloem, and the cork cambium produces cork.
6. As the diameter of the stem increases, the outermost tissues rupture and slough off from the stem.
7. Cork forms the outer bark.
8. The cork cambium and the cork form a layer of periderm.
9. The secondary phloem comprises inner bark .

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Secondary xylem that develop in the spring have relatively large diameters and are known as early wood. Tracheids and vessel elements produced in late summer or early fall are smaller and are known as late wood. The alternation of early and late wood give rise to growth rings in trunks.

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Cell division in the vascular cambium.

1. Types of cell division.

   A cambium cell can divide transversely to form more cambium cells (C) or radially to produce either xylem (X) or phloem (P) cells.
   
   
   

2. Accumulation of secondary growth.

   Repeated radial divisions build up layers of xylem and phloem. The cambium usually produces much more xylem than phloem.

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Anatomy of a tree trunk.

Periderm consists of the cork cambium plus the layers of cork cells it produces.

Bark consists of tissues external to the vascular cambium, including secondary phloem and periderm.

The older layers of secondary xylem (heartwood) no longer transport water and minerals, leaving that function to the outer sapwood.

In temperate regions, the vascular cambium becomes dormant during winter. When secondary growth resumes the next spring, the boundary between the large cells of the new early wood and the smaller cells of the late wood leaves distinct annual rings.

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Leaf anatomy.

The epidermis is interrupted by stomata each consisting of a pore flanked by two guard cells which regulate gas exchange.

The ground tissue ( mesophyll) is sandwiched between the upper and lower epidermis, made of parenchyma cells specialized for photosynthesis. The palisade mesophyll consists of elongated cells on the upper part of the leaf. The spongy mesophyll is loosely arranged, allowing CO₂ and O₂ to circulate.

Veins are the leaf's vascular bundles; each vein is enclosed by a protective bundle sheath consisting of parenchyma cells.

Many leaves have been modified to perform specialized functions.

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Simple versus compound leaves.

You can distinguish simple leaves from compound leaves by looking for axillary buds.

Each leaf has only one axillary bud, where the petiole attaches to the stem; a compound leaf consists of one petiole with several leaflets.

Each leaf is composed of several tissues .

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Three years' past growth evident in a winter twig.

Apical meristems, located at the tips of roots and in the buds of shoots, enable the plant to grow in length, a process known as primary growth.

Many grasses have intercalary meristems that allow them to regrow after being shortened by grazing animals or mowers.

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An overview of an idealized eudicot.

The plant body is divided into a root system and a shoot system, connected by vascular tissue (purple strands).

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Grouped in strands or cylinders, collenchyma cells have thick primary walls that support young parts of the plant shoot, such as the "strings" just below the epidermis in celery stalk.

Collenchyma cells provide flexible support as the stems elongate.

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Parenchyma cells have thin and flexible cell walls, and usually has a large central vacuole.

Parenchyma cells perform most of the metabolic functions of the plant, synthesizing and storing organic products.

The fleshy tissue of a typical fruit is composed mainly of parenchyma cells.

Many parenchyma cells retain the ability divide and differentiate into other cell types.

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Sugar-conducting cells of the phloem.

Phloem is made of living sieve-tube members that lack a nucleus, ribosomes, or vacuoles; their metabolic functions are provided by companion cells.

The end walls between cells (sieve plates) have pores for transport.

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Two types of sclerenchyma cells have thick, rigid secondary walls strengthened by lignin and are more .

Sclereids are short and irregular in shape and have thick secondary walls found in nutshells and seed coats, and give the gritty texture to pear.

Fibers are long and tapered and can be found in hemp and flax fibers for making rope and linen.

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Water-conducting cells of the xylem.

The tracheids and vessel elements are dead at maturity.

Water can move laterally through pits in the secondary walls.

Tracheids have tapered ends with pits, while vessel elements have perforated ends to allow water transport.

The secondary walls of tracheids also contain lignin to provide support.

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Root hairs and root tip.

Root hairs increase the surface area for the absorption of water and minerals by the roots.

Root tips are areas of meristemic growth.

Many plants exhibit special root adaptations .

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Modified roots. Environmental adaptations result in roots being modified for a variety of functions. Many modified roots are aerial roots that are above the ground during normal development.

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At the angle between a stems and the stem is an axillary bud that is usually dormant, while a terminal bud is located near the apex, where growth is concentrated, due to apical dominance.

Many plants have modified stems adapted for specialized functions.

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The three tissue systems.

The dermal tissue system (blue) covers the entire body of a plant.

The vascular tissue system (purple) is arranged differently in each organ.

The ground tissue system (yellow), responsible for most of the plant's metabolic functions, is located between the dermal tissue and the vascular tissue.