Final answer:
The number of leaves on a tree is a variable trait influenced by both environmental conditions like temperature and genetic factors.
Step-by-step explanation:
The number of leaves on a tree is influenced by temperature as well as various other environmental and genetic factors. Leaves can be considered a variable trait, as their number can change in response to external conditions such as the amount of water, plant food, soil quality, and sunshine the tree receives. Additionally, leaves are subject to genetic controls which can dictate their potential number, size, and shape.
For instance, if we look at experimental setups like Gary's, there are several factors he did not control that could vary, such as individual plant variation, soil temperature due to different colors of containers, water loss due to evaporation, and the effect of insects. Hence, the number of leaves is a characteristic that is dynamically affected by both genetics and the environment.