Selection and evolution: explain question

A researcher measured the stem heights (cm) of two varieties of sunflower grown in two different fields. She wanted to investigate whether the difference in mean height is due to genetic factors, environmental factors, or both. The table below shows the results.

The t-test formula is:

$$t = \frac{\bar{x}_1 - \bar{x}_2}{\sqrt{\frac{s_1^2}{n_1} + \frac{s_2^2}{n_2}}}$$

The calculated value of t is 5.2, which is significant at p < 0.01.

Explain the likely causes of variation within each sample and the difference between the two samples. Refer to the nature of the variation (discontinuous or continuous), the genetic basis of such variation, and the t-test result in your answer.