Ground Tissue System in Plants: Cortex, Pith Functions
The ground tissue system includes all tissues except the epidermis and the vascular bundles. It fills the body of the plant and forms regions like the cortex, endodermis, pericycle, pith, and medullary rays. It is mostly made of parenchyma, with collenchyma and sclerenchyma in places.
This system matters because it stores food and water, supports the plant, and in leaves performs photosynthesis. The soft edible parts of many vegetables and fruits are mainly ground tissue, so it links plant anatomy directly to food.
Key Concepts
- Cortex: Region between epidermis and vascular cylinder, mainly parenchymatous, for storage.
- Endodermis: Innermost cortex layer with Casparian strips controlling entry into the stele.
- Pericycle: Layer just inside endodermis; in roots it gives rise to lateral roots.
- Pith: Central ground tissue in stems and roots for storage.
- Mesophyll: Ground tissue of the leaf between upper and lower epidermis, packed with chloroplasts.
Ground tissue is simple in composition but performs storage, photosynthesis, and mechanical roles depending on location.
How It Works
- Outer cortex cells may contain chloroplasts in young stems and help in photosynthesis.
- Middle cortex stores starch and water for later use.
- Endodermis checks which substances pass into vascular tissues.
- Pith stores food and, in some plants, helps in internal support.
Worked Example
A stem section has a total radius of 10 mm. Cortex thickness is 3 mm, vascular region is 4 mm wide, and pith radius is 3 mm. Check: 3 + 4 + 3 = 10 mm. If pith cells store 2 mg starch per gram and pith mass is 5 grams, stored starch = 2 × 5 = 10 mg. Such estimates show storage capacity of ground tissue.
Common Misconceptions
- Ground tissue is only filler: Wrong. It actively stores, photosynthesises, and regulates transport.
- Pith and cortex are the same: Wrong. Cortex is outside the vascular cylinder; pith is central.
- Endodermis is part of vascular tissue: Wrong. It is the innermost layer of ground tissue (cortex).
Real-World Applications
Potato tuber, carrot, and fruit pulp are storage ground tissues eaten as food. Aerenchyma in aquatic plant ground tissue provides buoyancy. In medicine and industry, stored compounds in cortex and pith of stems are sources of fibres, gums, and some extracts.
Cortex outside, pith inside, and mesophyll in leaves — ground tissue is the working and storage bulk that makes plant bodies soft, green, and useful.