The phenomenon of delay of senescence by cytokinins is known as

Options

A. Richmond lang effect
B. Senescence of effect
C. Loomis and Torry effect
D. Sorokin et al effect , 1962

Answer

### Step-by-Step Solution:

1. **Understanding Cytokinins**: Cytokinins are a class of plant hormones that promote cell division and growth in plants. They are primarily synthesized in areas of the plant where rapid cell division occurs, such as in roots and developing fruits.

2. **Function of Cytokinins**: One of the key functions of cytokinins is to delay senescence, which is the process of aging in plants. This means that they help keep leaves and other plant parts alive and functioning for a longer period.

3. **Identifying the Phenomenon**: The specific phenomenon where cytokinins delay senescence is known as the Richmond Lang effect. This effect was named after the scientists Richmond and Lang, who identified this phenomenon in 1967.

4. **Conclusion**: Therefore, the phenomenon of delay of senescence by cytokinins is referred to as the Richmond Lang effect.

5. **Final Answer**: The correct answer to the question is option A: Richmond Lang effect.