Balance natural selection

Balancing selection is a type of natural selection that maintains genetic diversity in a population.

In balancing selection, two or more alleles are kept in balance, and therefore are  maintained in a population over the course of many generations.

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In monocotyledonous plants, the primary root is short lived and is replaced by a large number of roots called “Fibrous root system”

II.Fibrous root System

It develop from other than radicles

Many Small branching Roots, called fibrous root, but no large Primary root

The huge number of thread like roots increases the surface area for absorption of water and minerals

Fibrous root anchor the plant less securely

Fibrous root system

Fibrous root system found in Monocot Plants.

e.g., Maize, Paddy, Wheat, Grass, Onion

Families- Liliaceae, Poaceae etc.

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Modification of root

Storage roots

Epiphytic or Aerial absorbing Roots e.g., Orchids.

Assimilatory roots

Respiratory roots or pneumatophores

Sucking roots or haustoria

Storage roots

Tap roots of carrot, radish, turnip and adventitious roots of sweet potato, dahlia get swollen and store food

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1. Prop Roots- hanging structures that support a banyan tree

Stilt roots of Sugarcane and Maize are supporting roots which arise from the lower nodes of the stem. These roots grow downwards and penetrate the soil and provide mechanical support to the plant.

Ex- Sugarcane  

3.Climbing roots

climbers can climb up their supports as adventitious roots growing from the nodes.

e.g., Pothos (money plant)

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Modification of stem

I.Aerial stem modification

Aerial modification can be classified into tendrils, thorns, and phylloclade. 

Stem tendrils which develop from axillary buds, are slender and spirally coiled and help plants to climb such as in gourds (cucumber, pumpkins, watermelon) and grapevines

I.Aerial stem modification

Some plants of arid regions modify their stems into flattened (Opuntia), or fleshy cylindrical (Euphorbia) structures. They contain chlorophyll and carryout photosynthesis.

Example- Cactus (Opuntia), Sparrow grass (Asparagus), etc. 

I.Aerial stem modification

Axillary buds of stems may also get modified into woody, straight and pointed thorns, hard, spiny structure protect plants from grazing animals.

Found in many plants such as- Pomegranate (Punica granatum), Paper flower (Bougainvillea glabra), Lemon (Citrus limon), etc.

II.Subaerial Stem modification

Subaerial modification can be classified into four types, namely stolon, runner, sucker, and offset. 

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