Asexual reproduction produces new plants from a single parent without the involvement of gametes. The offspring are genetically identical to the parent plant (clones).

Common Methods of Asexual Reproduction

1. Vegetative Propagation This occurs through specialized plant structures such as:

• Runners (stolons): Horizontal stems that grow along the ground surface, producing new plants at nodes. Example: Strawberry and grass plants.
• Tubers: Underground swollen stems that store food. Example: Irish potato - eyes on the tuber grow into new plants.
• Bulbs: Underground storage organs with fleshy leaves. Example: Onion and garlic.
• Rhizomes: Underground horizontal stems. Example: Ginger and canna.
• Corms: Short, swollen underground stems. Example: Cocoyam (vija*.
• Suckers: Shoots that arise from underground roots. Example: Banana and orange trees.

2. Grafting and Budding A horticultural technique where a piece of one plant (scion) is attached to the rootstock of another plant. This is common in fruit trees like mangoes and citrus.

3. Tissue Culture (Micropropagation) A modern technique where plant cells are grown in a sterile nutrient medium to produce many identical plants. This is used commercially for crops like sugarcane and cassava.

Sexual reproduction involves the fusion of male and female gametes, producing offspring with genetic variation. In flowering plants (angiosperms), this process occurs within the flower.

Structure of a Flower

A typical flower contains both male and female reproductive parts:

Male Part (Stamen)

• Anther: Produces pollen grains containing male gametes
• Filament: Supports the anther

Female Part (Carpel or Pistil)

• Stigma: sticky tip that receives pollen
• Style: Tube connecting stigma to ovary
• Ovary: Contains ovules (female gametes)
• Ovule: Contains the egg cell

Supporting Parts

• Sepals (Calyx): Green outer leaves that protect the flower bud
• Petals (Corolla): Brightly colored leaves that attract pollinators
• Receptacle: Base of the flower where all parts attach

Definition

Pollination is the transfer of pollen grains from the anther (male part) to the stigma (female part) of a flower. This is a necessary step for sexual reproduction in flowering plants.

Types of Pollination

1. Self-Pollination This occurs when pollen from an anther lands on the stigma of the same flower or another flower on the same plant.

• Examples: Garden peas, wheat, dandelion

2. Cross-Pollination This occurs when pollen is transferred from the anther of one plant to the stigma of a different plant of the same species.

• Examples: Maize, sunflower, sugarcane

Agents of Pollination

Pollination is aided by external agents:

Wind

• Pollen grains are small, light, and abundant
• Flowers are small, not brightly colored, with feathery stigmas
• Examples: Maize, rice, grass

Insects

• Flowers are brightly colored and produce nectar
• Pollen grains are sticky and have spiky surfaces
• Examples: Hibiscus, beans, sunflower

Other Agents

• Birds (e.g., honeycreepers)
• Bats
• Water (in some aquatic plants)

Process of Fertilization

After successful pollination, the following events occur:

1. Pollen Germination: When a pollen grain lands on a compatible stigma, it absorbs sugary secretions and germinates.

2. Pollen Tube Growth: A pollen tube grows from the pollen grain, traveling through the style toward the ovary.

3. Entry into Ovule: The pollen tube enters the ovule through a tiny opening called the micropyle.

4. Release of Male Gametes: The pollen tube bursts, releasing two male gametes into the embryo sac.

Double Fertilization

This is a unique process in flowering plants:

1. First Fusion: One male gamete fuses with the egg cell nucleus to form a diploid zygote (2n), which develops into the embryo.

2. Second Fusion: The other male gamete fuses with the two polar nuclei to form a triploid nucleus (3n), which develops into the endosperm (food storage tissue).

This process is called double fertilization because two separate fusions occur.

After fertilization:

• The ovule develops into a seed
• The ovary develops into the fruit
• The zygote develops into an embryo with:
  • Plumule (young shoot)
  • Radicle (young root)
  • Cotyledons (seed leaves)

The endosperm provides food for the developing embryo. Other flower parts (petals, sepals, stamens) wither and fall off.

In Tanzania, understanding plant reproduction is essential for farming. For example, when a farmer grows beans (a common legume in Mbeya and many other regions), knowledge of pollination helps them understand why planting only one bean variety in an isolated area may result in poor pod formation. If cross-pollination is needed, farmers can attract pollinators like bees by keeping beehives near bean farms, which can improve yields and increase harvest — potentially earning a farmer an extra TZS 200,000 to 500,000 per season from better bean production.