Growth of plant tissues in artificial media is

The correct option is plant tissue culture.

Let us break down the explanation step-by-step to understand why this option is correct:
1. Definition of Plant Tissue Culture: Plant tissue culture is a collection of techniques used to maintain or grow plant cells, tissues, or organs under sterile (aseptic) conditions on a nutrient culture medium of known composition. In other words, it is the growth of plant tissues in artificial media.
2. Understanding the other options:
- Cell hybridization: This is the process of fusing two different cells (often from different species) to form a single hybrid cell. It does not refer to the general growth of plant tissues in artificial media.
- Transgenesis: This is the process of introducing an exogenous gene (a transgene) into a living organism so that the organism will exhibit a new property and transmit that property to its offspring.
- Gene expression: This is the process by which information from a gene is used in the synthesis of a functional gene product, typically proteins.

Therefore, the technique specifically defined by the growth of plant tissues in an artificial, nutrient-rich medium is indeed plant tissue culture.