Classification of stems according to the degree of lignification
1. Herbaceous stems are found in herbaceous plants and young shoots of trees. Herbaceous stems usually exist for one season. Dandelion officinalis is a typical representative of herbaceous plants with a green, succulent stem. The giant hogweed has a hollow stem.
2. Woody stems are found in trees and shrubs. They acquire hardness due to the deposition in the membrane of their cells of a special substance – lignin.
Lignification occurs in the stems of trees and shrubs from the second half of the summer of the first year of their life. Their wood forms annual rings. All layers of wood cells formed in spring, summer and autumn form an annual growth ring. A ring formed in one growing season is called an annual ring. By the number of rings, you can determine the age of the tree.
Small autumn cells differ from large spring wood cells next year, which are next to them.
Therefore, the border between adjacent growth rings on the cross section of wood is clearly visible in many trees.
By counting the number of tree rings with a magnifying glass, you can determine the age of a sawn tree or branch cut.
By the thickness of the growth rings, you can find out in what conditions the tree grew in different years of life. Narrow growth rings indicate a lack of moisture, shading of the tree and its poor nutrition.
Under good development conditions, the annual rings are wider.
Classification of stems according to the direction of growth
Plant stems can be positioned differently in relation to the soil and adjacent plants. Allocate erect, creeping, ascending, clinging and curly stems.
Erect stems grow vertically upward and do not need any support.
Example: such stems are in sunflower, bellflower, nettle, hedgehog, woody plants
Creeping stems spread along the ground and take root in the soil with adventitious roots.
Example: such stems develop in strawberries, clover, meadow tea, cinquefoil goose
The grasping stems rise upward, attaching themselves to the support.
Example: they can be attached by antennae (peas, mouse peas, cucumber, rank, grapes), or by hook roots (ivy)
Curly stems bring leaves to the light, twisting around erect stems or artificial supports.
Example: bindweed, common hops
Plants with clinging and climbing shoots are called vines.