基本植物解剖学：根、茎和叶

Plants are often perceived as less complex than animals, but much like animals, they are made up of organs and organ systems that perform specialized functions.

The vast majority of plants have two organ systems: the shoot and root systems. Roots typically grow underground. They anchor the plant and take up water and nutrients from the environment. The two major types of root systems are taproot systems and fibrous root systems. 

In a taproot system, a primary root emerges from the seed upon germination and grows deep into the soil to anchor the plant. Much smaller lateral roots then branch off of the primary root.

In a fibrous root system, however, the primary root supports only seedling development. Later, many thin roots branch from the stem underground. These so-called adventitious roots form a shallow network in the soil that supports the mature plant.

The organs that comprise the shoot system can be classified as either reproductive or vegetative organs. The reproductive organs include flowers, fruit, and cones. There is considerable diversity in how plants reproduce and consequently in the reproductive organs that they possess. The vegetative organs, however, always include stems and leaves.

The stem of a plant provides structure, supporting the leaves, buds, and flowers. The stem also orients the leaves to maximize photosynthesis. Stems are composed of nodes, points at which leaves and branches attach, and internodes, the regions of stem between the nodes. 

A stalk called a petiole anchors each leaf at the node. The terminal part of the leaf is called the blade or lamina. Simple leaves have one blade per petiole, while compound leaves have multiple blades attached to each petiole. Still other plants, such as grasses, lack a petiole. Instead, the blade directly envelops part of the stem.

The leaves conduct the majority of photosynthesis. The blades are often thin and flattened in shape to maximize the surface area exposed to sunlight.