{"id":5010,"date":"2022-01-22T18:48:44","date_gmt":"2022-01-22T18:48:44","guid":{"rendered":"https:\/\/www.guyhowto.com\/?p=5010"},"modified":"2022-01-13T11:30:36","modified_gmt":"2022-01-13T11:30:36","slug":"theories-of-organization-of-cells-in-apical-meristem","status":"publish","type":"post","link":"https:\/\/www.guyhowto.com\/theories-of-organization-of-cells-in-apical-meristem\/","title":{"rendered":"Theories of Organization of Cells in Apical Meristem"},"content":{"rendered":"
Theories of Organization of Cells in Apical Meristem<\/strong><\/h5>\n

The region of actively dividing cells that form roots and are capable of division is called apical meristems. The cells in the meristem are thin-walled and densely filled with granular contents. There are three most important concepts about the organization of cells in apical meristems. These are given below:<\/p>\n

Apical Cell Theory<\/strong><\/h5>\n

Apical cell theory was put forward by Von N\u00e4geli<\/strong> in 1858. Apical cells were discovered in pteridophytes. It was believed that such cells also exist in seed plants. The apical cells were taken as the constant structural and functional units of apical meristems. They govern the whole process of growth. But later it was confirmed that this theory is only applicable to pteridophytes.<\/p>\n

\"Apical-Cell-Theory\"<\/p>\n

Researchers further have refuted the universal occurrence of apical cells. They replaced it with another theory of the independent origin of different parts of the plant body. This theory is known as the Histogen theory.<\/p>\n

Histogen Theory<\/strong><\/h5>\n

Hanstein<\/strong> in 1870, put forwarded histogen theory. He said that apical meristem is separable into three distinct zones or Histogens. This theory states that apical meristem is the growing region of stem and root which is composed of a small mass of cells. These calls are all alike and in a continuous state of division. These meristematic cells constitute promeristem.<\/p>\n

The cells of the promeristem soon differentiate into three regions dermatogen, periblem, and plerome. Every zone consists of initials and is called histogen or tissue builder.<\/p>\n

\"Histogen-Theory\"<\/p>\n

Objections on the Theory<\/strong><\/h5>\n

In later studies and investigations, researchers found that there is no strict relationship between the development of historians and various regions of the plant body.<\/p>\n

This theory does not provide cytological proof.<\/p>\n

The distinction of these histogens in the apex cannot be made in some plants. The other regions do not show any morphological significance.<\/p>\n

Tunica Corpus Theory<\/strong><\/h5>\n

In 1924, Schmidt advocated this theory. It replaced the histogen theory basically due to the lack of cytological proof. This theory states that the dividing cells in the apical meristems are arranged in two zones.<\/p>\n

Tunica:<\/strong><\/h5>\n

The outer zone is called tunica which is composed of one or two layers of superficial cells. The cells of tunica divide and clinically. It forms two-layer thicknesses. Monocots have single layered tunica were as dicots have two layered tunicae. The epidermis arises from the outer layer of the tunica.<\/p>\n

\"Tunica\"<\/p>\n

Corpus:<\/strong><\/h6>\n

The central zone is called the corpus. The cells are large in corpus and the mass of corpus cells is covered by tunica cells. The cells of the corpus divide in all planes and thus the whole mass grows in volume. Inner tissues like cortex and vascular tissues are derived from both tunica and corpus.<\/p>\n

Two zones can be distinguished in tunica. The first is the central apical zone with one or a few initials. The cells are large with large nuclei and vacuoles. The second zone is present on the sides of the apex between the initials and the leaf primordia. This zone consists of small, darkly, stained cells which divide more frequently.<\/p>\n

Drawbacks of Tunica Corpus Theory<\/strong><\/h5>\n

This theory is widely accepted but it cannot characterize the apical meristems of gymnosperms. Shoot apices of a few gymnosperms have independently propagating layers. It is like tunica. In others, the outermost layer divides periclinally.<\/p>\n

Histogen Layer Theory<\/strong><\/h5>\n

In 1977, Derman put forward this theory. He proposed the concept of primary histogenic layers. According to this theory, there are three basic histogenic layers in angiosperms. He named them L-I, L-II, L-III. The L-I gives rise to the epidermis. The L-II gives rise to the cortex. The L-III gives rise to vascular tissues and pith.<\/p>\n

\"Histogen-Layer-Theory\"<\/p>\n

 <\/p>\n","protected":false},"excerpt":{"rendered":"

The region of actively dividing cells that form roots and are capable of division is called apical meristems. The cells in the meristem are thin-walled and densely filled with granular contents.<\/p>\n","protected":false},"author":2,"featured_media":5012,"comment_status":"closed","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[16],"tags":[],"yoast_head":"\nTheories of Organization of Cells in Apical Meristem<\/title>\n<meta name=\"description\" content=\"The region of actively dividing cells that form roots and are capable of division is called apical meristems. 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