The rate of three phases of growth in plants can be explained by...

The growth of a plant or its parts typically shows three distinct phases: lag phase, $\log$(exponential) phase, and stationary phase.

In the lag phase, growth is slow. In the log phase, growth is rapid and exponential. In the stationary phase, growth slows down and eventually stops as the plant reaches maturity or resources become limited.

When the rate of growth is plotted against time, these three phases form an S-shaped or sigmoid curve. Therefore, the rate of three phases of growth in plants is explained by a sigmoid graph.

Answer: sigmoid