The poison of poison ivy, oak, and sumac is an oleoresin. In which part of the plant is this oleoresin NOT found?

The oleoresin found in poison ivy, oak, and sumac, which contains the irritating compound urushiol, primarily exists in the leaves, flowers, and stems of these plants. The leaves are well-known for containing high concentrations of this substance, and the flowers also carry oleoresin as part of the plant's defensive mechanism. The bark, while not a primary source, can contain lower levels of oleoresin as it is part of the plant’s structure.

However, the wood of these plants does not typically contain significant amounts of oleoresin. Instead, the wood is primarily composed of xylem tissue, which serves different functions in the plant, such as support and water transport. Therefore, the choice that identifies where the oleoresin is not found is indeed the wood, as it is not a storage or secretion site for this irritant compound.