Plant Forms and Functions

Understanding the forms and functions of crop plants is central to successful agricultural production. This guide covers the anatomical and morphological structures of crop plants, focusing on the differences between monocotyledonous and dicotyledonous crops, as well as the specialized storage organs they use to store food.

1. Parts of Crop Plants and Their Functions

A typical crop plant is divided into two main systems: the Shoot System (above the ground) and the Root System (below the ground).

• The Root System: Consists of primary, secondary, and tertiary roots. It functions in anchoring the plant firmly in the soil, absorbing water and dissolved mineral salts from the soil, and in some cases, storing food.
• The Stem: Serves as the main structural axis of the plant. It supports the leaves, flowers, and fruits, conducts water and minerals from the roots to the leaves via the xylem, and transports manufactured food from the leaves to other parts of the plant via the phloem.
• The Leaf: The primary site of photosynthesis. It contains chlorophyll which traps sunlight to synthesize carbohydrates. It also facilitates transpiration (water loss) and gaseous exchange through tiny pores called stomata.
• The Flower: The reproductive organ of the plant. It contains the male reproductive organ (androecium made of stamens) and the female reproductive organ (gynoecium made of pistils/carpels). Flowers produce seeds and fruits after fertilization.
• Seeds and Fruits: Protect the developing embryo and aid in the dispersal of the plant species to new locations.

2. Distinguishing Between Monocot and Dicot Crop Plants

Crop plants are botanically classified into two major classes based on the number of embryonic leaves (cotyledons) present in their seeds:

3. Anatomy and Morphology of Storage Organs

Many crop plants store manufactured food (mostly carbohydrates/starch) in specialized modified organs. These structures allow the plant to survive adverse environmental conditions (perennation) and serve as valuable food sources for humans and livestock.

A. Root Tubers

These are modified lateral or primary roots that swell with accumulated starch. Unlike stems, they do not possess nodes, internodes, or scale leaves.

• Cassava (Manihot esculenta): A modified adventitious/lateral root system. Internally, a cross-section reveals an outer cork layer, a thin cortex, and a large central starch-storing parenchymatous region.
• Sweet Potato (Ipomoea batatas): Modified adventitious roots containing high levels of starch and sugars.

B. Stem Tubers

These are swollen underground stems. Unlike root tubers, stem tubers possess characteristics of stems, such as "eyes" (which are actually auxiliary buds at the nodes protected by tiny scale leaves).

• Yam (Dioscorea spp.): Modified underground stem structure. It serves as a storage organ and also as a means of vegetative propagation.
• Irish Potato (Solanum tuberosum): A classic stem tuber showing distinct eyes (buds) from which new shoots sprout.

C. Rhizomes

These are horizontally growing underground stems with distinct nodes, internodes, lateral buds, and dry scale leaves.

• Ginger (Zingiber officinale): Stores food in its fleshy horizontal stem. It propagates easily from small sections containing buds.

D. Corms

These are swollen, vertically growing underground solid stems wrapped in thin, dry scale leaves.

• Cocoyam (Colocasia esculenta): The corm is the main storage organ, containing high amounts of starch crystals. It features distinct circular nodes where scale leaves attach.

E. Bulbs

These are short, underground shoots surrounded by fleshy, layers of scale leaves that store water and nutrients.

• Onion (Allium cepa): The true stem is a flattened disc at the bottom. The edible storage parts are actually modified leaf bases (fleshy scale leaves) wrapped around a central terminal bud.