Plant Morphology - 1

An oblong leaf has parallel sides. The leaf has a rectangular shape with rounded corners. An example of this kind of leaf is willow.

In vascular plants, the root is the organ of a plant that typically lies below the surface of the soil. This is not always the case, however, since a root can also be aerial (growing above the ground) or aerating (growing up above the ground or especially above water). It produces endogenous branches.

Leaves are the physical platform for the process of photosynthesis. Leaves function to capture carbon dioxide and sunlight to produce carbohydrates (sugar, starch and cellulose [or wood]), while minimizing water loss.

Isobilateral leaves, which are flat leaves without an upper or lower surface. Ordinary (dorsiventral) plant leaves have an upper, harder surface which faces the sun, and a lower shade-surface where most of the carbon dioxide and water vapour exchange takes place. Isobilateral leaves exchange carbon and water equally through both surfaces, but at a lower rate than dorsiventral leaves.

The roots of the tree absorb both water and mineral nutrients for use in the rest of the tree. The root hairs which are found in most tree species are especially important in the absorption of these products by the roots.

Stems that run horizontally below the ground surface are termed rhizomes.For example,Rhizomes of Johnson grass, a weedy species commonly found in various areas.

These are the regions of parenchyma tissue separating the individual vascular bundles of the dicot stem.

The central portion of the stem is filled with parenchyma cells that have very distinct intercellular spaces; this region is collectively known as the pith.

The pericycle is made up of sclerenchyma cells which are lignified, dead fibre cells . These cells have thick, woody walls and tapering ends. Functions of the Pericycle: It strengthens the stem. It provides protection for the vascular bundles.

The vascular bundles are found scattered throughout the ground tissue. The vascular bundles occurring nearer the ring of the stem are smaller and are closer to one another. The vascular bundles contain no cambium and consequently secondary thickening does not occur.

Some orchids like Vandas are epiphytic and grow on trees without hurting them. The orchids derive moisture and nutrients from the air and rain with their aerial roots that can be a few yards long. Older roots have a spongy outer layer called a velamen that can absorb moisture in the air and make it available to the plant. Some have chlorophyll so can manufacture food for the orchid.

Trees that are found in tidal areas are often called mangroves. Black mangroves survive by producing straw-like roots called pneumatophores that stick out of the soil to take in oxygen. The pneumatophores can grow over nine feet tall and may be combined with buttress roots to give support.

All of the above have tap roots.

Ferns, iris, and bent grass produce horizontal underground stems known as rhizomes. Leaves grow at one end and roots at the other. They can be fleshy like those of ferns and German iris and serve as important storage organs for the plant. Rhizomes are often used to propagate plants.

The pith occupies the large central part of the stem. It consists of thin-walled parenchyma cells with intercellular air spaces. Between each vascular bundle is a band of parenchyma, the medullary rays, continuous with the cortex and the pith. Functions of the Pith or Medulla: the cells of the pith store water and starch. They allow for the exchange of gases through the intercellular air spaces.

African violets and dandelions have crowns, that is compressed stems with leaves and flowers on short internodes.

A phyllode is the petiole or rachis of a leaf which is modified into a green flat structure for the purpose of photosynthesis. In such a leaf, the lamina is poorly developed. In Acacia melanoxylon, the petiole is flattened, green and becomes a phyllode. The leaflets and secondary rachii drop off.

A phylloclade is a flattened stem of several internodes functioning as a leaf. In Opuntia the stem is modified into a green flattened structure called Phylloclade. On the surface of the phylloclade, clusters of spines are formed. These spines are the modified leaves of the auxilliary bud. These spines not only check the rate of transpiration but also protect the plant from herbivores. The phylloclade has distinct nodes and internodes. E.g., Opuntia.

Epidermis is in two layers, one on each surface of the leaf. Both the epidermal layers are composed of compactly arranged, barrel shaped cells. Cuticle and trichomes are present in both the layers. Stomata are found in both the epidermal layers. This condition is described as amphistomatic. A few cells in the upper epidermis are enlarged to form motor cells called bulliform cells.

Veins represent the vascular bundles. They are found irregularly scattered in the mesophyll due to reticulate venation. The largest and the oldest vein is found in the centre. It is known as midrib vein.

When a leaf has more than one leaf blade on a stalk,  it is called as a compound leaf. The multiple leaf blades are known as leaflets. The leaflets together make a single leaf that is attached to a single stalk. Like a simple leaf, the stalk of a compound leaf is also attached to the plant body and it leaves a scar mark on the plant body when it is removed from the stem.

Carotenoids are very long-chain water-repelling pigments that are synthesized in the plastids of plant cells. These pigments primarily absorb  the blue wavelengths, allowing the longer wavelengths to be scattered and producing the yellow colour.

Some plants like morning glories and black eyed Susan vine have twining stems that climb by wrapping themselves around another object.

A bulb is part modified stem, part modified leaves. The stem portion is compressed and its central terminal bud is surrounded by fleshy modified leaves. Onions, tulips, and daffodils all produce true bulbs. Next time you cut an onion in half longitudinally, look in the centre for the terminal bud.