Botany and Plant Science

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.

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.

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.

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.

It is a fleshy product of a tree or plant that derives from flowers.

It is a condition in which male reproductive organ matures before female reproductive organ.

It provides nourishment to pollen grains.

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