Why is not any one parameter good enough to demonstrate growth throughout the life of a flowering plant?
Growth in flowering plants is measured by various parameters such as increase in fresh weight, dry weight, length, area, volume, and cell number. However, different plants and plant parts express growth differently.
For instance, in a maize root apical meristem, growth is expressed as increase in cell number (more than 17,500 new cells per hour). In contrast, cells in a watermelon increase in size by up to 3,50,000 times. Similarly, growth of a pollen tube is measured in terms of its length, while growth in a dorsiventral leaf is denoted by increase in surface area.
Since different plant parts show growth through different parameters at different stages of the plant's life, no single parameter is sufficient to demonstrate growth throughout the entire life of a flowering plant.
Explanation
The textbook (section 13.1.2) clearly explains that growth is measured by multiple parameters because different plants and plant organs express growth differently. The maize root shows growth through cell number increase, watermelon through cell size expansion, pollen tube through length, and leaf through surface area. This diversity in growth expression across different plant parts and stages means no single parameter can adequately capture growth throughout a flowering plant's complete life cycle.