Internal Structure of the Stem
Internal Structure of the Stem
The internal structure of the stem is usually more complex than the other plant organs for it performs and provides various functions. These functions are: * For mechanical support * For conduction of water * For conduction and storage of manufactured food * For continuous growth of the stem in thickness
These functions are centered at the fibro vascular system that is composed of two major tissues, the xylem and the phloem.
Internal Parts of Woody Stems 1. Protective layers
In a young plant, the protective covering is the epidermis but then as the plant matures, the epidermis is sloughed off and will be replaced by the cells that originate from the cork cambium or phellogen. This produces a layer of cork cells which are suberized, thus almost impermeable to air or water. But, there are small areas in which the cells are loose and spongy that allow a small amount of gaseous interchange. These areas are called lenticels.
2. Cortex and Pith
These two are very similar in character. Their cells are the isodiametric parenchyma cells that have cellulose walls and function chiefly in the storage of food. Collenchyma comprises the outer layer of the cortex. 3. Endodermis and Pericycle
The endodermis is the innermost cell layer of the cortex. It is almost indistinguishable from the other cortical cells, but sometimes it can be recognized if the Casparian strip is visible.
Endodermal cells are packed with starch grains.
The pericycle, on the other hand, is the outermost layer of the vascular bundle, in between the endodermis and the phloem. This is often hard to distinguish from adjacent cells. It is composed of thick-walled fibers which are scattered irregularly and the rest of it is parenchyma tissues. 4. Phloem
This is the main mode of transportation of manufactured food in plants. The cells responsible for this are the sieve tubes, the elongated living cells with cellulose walls, having no nucleus.
The internal structure of the stem is usually more complex than the other plant organs for it performs and provides various functions. These functions are: * For mechanical support * For conduction of water * For conduction and storage of manufactured food * For continuous growth of the stem in thickness
These functions are centered at the fibro vascular system that is composed of two major tissues, the xylem and the phloem.
Internal Parts of Woody Stems 1. Protective layers
In a young plant, the protective covering is the epidermis but then as the plant matures, the epidermis is sloughed off and will be replaced by the cells that originate from the cork cambium or phellogen. This produces a layer of cork cells which are suberized, thus almost impermeable to air or water. But, there are small areas in which the cells are loose and spongy that allow a small amount of gaseous interchange. These areas are called lenticels.
2. Cortex and Pith
These two are very similar in character. Their cells are the isodiametric parenchyma cells that have cellulose walls and function chiefly in the storage of food. Collenchyma comprises the outer layer of the cortex. 3. Endodermis and Pericycle
The endodermis is the innermost cell layer of the cortex. It is almost indistinguishable from the other cortical cells, but sometimes it can be recognized if the Casparian strip is visible.
Endodermal cells are packed with starch grains.
The pericycle, on the other hand, is the outermost layer of the vascular bundle, in between the endodermis and the phloem. This is often hard to distinguish from adjacent cells. It is composed of thick-walled fibers which are scattered irregularly and the rest of it is parenchyma tissues. 4. Phloem
This is the main mode of transportation of manufactured food in plants. The cells responsible for this are the sieve tubes, the elongated living cells with cellulose walls, having no nucleus.