Spines primarily have a protective function in plants. The spines can be sharp, and form a physical barrier against herbivores which may want to feed on the plant. Spines however also have other benefits. The spines on a jumping cactus allow segments of the cactus to stick to passing large animals or humans, thereby allowing the cactus to spread to other areas through asexual propagation. Spines are modified leaves, and spines have a much lower surface area than leaves, and therefore can reduce transpirative loss of water by the plant during harsh droughts. Some trees in alpine regions, such as pine trees, have developed spine-like leaves to prevent the accumulation of snow in the branches.
A federal government is the type of government that combines aspects of both unitary and confederal government. The United States has a federal government.
