A student investigated the effect of light intensity on the growth of beech tree (Fagus sylvatica) leaves. They measured the maximum width of five leaves collected from a heavily shaded understory and five leaves from the sunny outer canopy.
| Leaf | Width in shaded understory (mm) | Width in sunny outer canopy (mm) |
|---|---|---|
| 1 | 62 | 44 |
| 2 | 58 | 40 |
| 3 | 65 | 42 |
| 4 | 57 | 45 |
| 5 | 63 | 39 |
| Mean | 61 | 42 |
Explain the difference in the mean width of beech leaves found in the shaded understory compared to those in the sunny outer canopy.