Why Do Plants of the Same Species Vary in Height?

In different environments plants of the same species can grow to varying heights. Why is this possible? The wheat, maize or millet sown in fertile and moist land grows high and stur-dy, while those sown at the same time, but in arid and infertile land are short and sparse. A tree growing alone can get sufficient sunshine and stretch out its branches more widely than a tree growing in a crowded wood. When trees of the same species grow together in a forest, the only way to get sufficient sunshine is to grow fall. This means trees growing in a forest are taller than those of the same species growing in a sparse field. Generally speaking, trees growing on mountains are thinner and shorter than trees growing on a plain, because the smaller size can withstand strong wind, which occurs more frequently in the mountains.