The correct answer is option 'A' - Flat.

The stratum germinativum, also known as the stratum basale, is the innermost layer of the epidermis, the outermost layer of the skin. It is composed of a single layer of columnar cells that are highly active in the process of cell division. These cells play a crucial role in the continuous renewal and regeneration of the epidermis.

The process of cell division in the stratum germinativum leads to the formation of new cells. As new cells are produced, the older ones are pushed upwards towards the surface of the skin. This process is known as keratinization.

The older cells, as they are pushed upwards, undergo several changes in their structure and composition. One of the key changes is the flattening of these cells. The columnar cells of the stratum germinativum gradually transform into flat, squamous cells as they migrate towards the surface of the skin.

This transformation is a result of the accumulation of keratin, a fibrous protein that provides structural support and protection to the skin. As the cells move upwards, they synthesize and accumulate more keratin, which causes them to flatten and lose their columnar shape. The accumulation of keratin also leads to the formation of a tough, waterproof barrier on the surface of the skin.

The flattened cells of the stratum germinativum, now known as the stratum corneum, form the outermost layer of the epidermis. This layer acts as a protective barrier against external factors such as pathogens, UV radiation, and chemical irritants.

In conclusion, the cells of the stratum germinativum are initially columnar and highly active in cell division. However, as new cells are formed and older cells are pushed upwards towards the surface of the skin, they undergo a transformation and become flat, squamous cells. This transformation is a result of the accumulation of keratin and is essential for the formation of a protective barrier on the skin.