What type of growth results in the increase of a tree's height?

The increase in a tree's height is primarily due to primary growth. This type of growth occurs at the tips of roots and shoots and is responsible for the elongation of these plant parts. The growth is driven by the activity of the meristematic tissues—specifically, the apical meristem located at the terminal end of the plant. As these cells divide and differentiate, they contribute to the extension of the stem and roots upward and downward, respectively.

Primary growth allows for the tree to reach towards sunlight and expand its root system deeper into the soil for water and nutrients. This is essential for the overall growth and health of the tree, as it not only increases height but also enhances its ability to photosynthesize and access necessary resources.

While other growth forms such as secondary growth—responsible for increasing the thickness of the trunk and branches—or lateral growth—expansion of the tree's width—play significant roles in a tree's overall development, they do not contribute directly to height increase like primary growth does. Thus, the focus on the apical meristem's role in height growth distinguishes primary growth as the correct answer.