Answer:

The method that renders the seed coat permeable to water so that embryo expansion is not physically retarded is called scarification.

Scarification:
Scarification is a process that involves intentionally damaging or weakening the seed coat to allow water to penetrate and promote germination. It is a common technique used to overcome seed dormancy in many plant species. The purpose of scarification is to break or soften the hard outer seed coat, which often hinders water absorption and restricts embryo growth.

Seed Coat Permeability:
The seed coat acts as a protective layer surrounding the embryo and endosperm in a seed. It is designed to prevent water from entering the seed and initiating germination until favorable conditions are present. However, in some cases, the seed coat can be too hard or impermeable, leading to delayed germination or even the inability of the seed to sprout.

Methods of Scarification:
There are several methods of scarification that can be used to enhance seed coat permeability. These methods include:

1. Mechanical Scarification: This involves physically damaging the seed coat using abrasion, filing, or sanding. The outer layer of the seed coat is scratched or removed to create small openings through which water can enter.

2. Chemical Scarification: Chemical scarification involves treating the seeds with chemicals or acids that soften or dissolve the seed coat. This method is often used for seeds with hard or thick seed coats that are difficult to mechanically scarify.

3. Hot Water Scarification: In this method, seeds are soaked in hot water for a specific period of time. The heat helps to soften the seed coat and promote water absorption.

4. Acid Scarification: Acid scarification involves treating the seeds with a mild acid solution, such as sulfuric acid or hydrochloric acid. The acid breaks down the seed coat, allowing water to penetrate.

Benefits of Scarification:
Scarification is an important technique in horticulture and seed propagation because it helps overcome seed dormancy and promotes faster and more uniform germination. By making the seed coat permeable to water, scarification allows the embryo to expand and grow without physical restriction. This ensures that the seed can successfully germinate and establish into a healthy plant.

In conclusion, scarification is the method used to render the seed coat permeable to water, allowing for proper embryo expansion and preventing physical retardation of growth. It involves damaging or weakening the seed coat through mechanical, chemical, or heat treatments, thereby promoting germination and overcoming seed dormancy.