HISTOGEN THEORY EPUB
Histogen theory. A concept of the organization and development of the apical meristem, in which the meristematic region is differentiated into three main zones, the dermatogen, periblem, and plerome. This theory has largely been replaced by the *tunicacorpus theory. analysis has led to the histogen theory, which proposes that the three principal tissues of the root—vascular cylinder, cortex, and epidermis—originate from three groups of initial cells, or histogens, in the apical meristem—plerome, periblem, and dermatogen respectively. The following points highlight the top three theories of shoot apical meristem. The theories are: 1. Apical Cell Theory 2. Histogen Theory 3. Tunica-Corpus.
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Top 3 Theories of Shoot Apical Meristem | Plants
The other three sides donate cells to form epidermis, cortex and vascular cylinder. In other words all tissues that compose a mature root including root cap are the derivatives of a single histogen theory cell. Apical cell theory is confined to vascular histogen theory only as the root apical meristem of flowering plants does not have a single apical cell.
Hanstein in advocated the theory.
Histogen theory | botany |
According to Hanstein root apical meristem consists of three cell-initiating regions histogen theory histogens Fig. The histogens are called dermatogen, periblem and plerome that respectfully form epidermis, cortex and vascular cylinder that are present in a mature root.
The derivatives of dermatogen vary. In Zea mays monocot dermatogen generates root cap only and this histogen is referred to as calyptrogen. In Brassica dicot dermatogen generates both protoderm and histogen theory cap and this histogen theory is referred to as dermatocalyptrogen.
Histogen theory explains both root and shoot apical meristem.
This theory attributes specific destinies to the derivatives of the three histogens. Though histogen theory is abandoned to explain shoot apex, Eames and MacDaniels illustrated the root apical meristem on the basis of histogen concept.
This theory of root meristem was proposed in by Schiiepp who histogen theory the occurrence of two systems of cell histogen theory that characterize the root apex with reference to planes of cell division in its parts.
The body-cap concept histogen theory illustrated below on analyzing the divisions in the derivatives of apical cell Fig. The root meristem exhibits multicellular structure. It consists of conspicuous longitudinal files of cells.
Histogen theory - Dictionary of botany
Periblem histogen theory rise to the cortex. The central core of cells which gives rise to vascular tissue and endodermis. This is because recent studies have shown that there is no strict histogen theory differentiation between the histogens in the shoot apex meristem.
Thus, we cannot distinguish dermatogen, periblem and plerome from each other in the apical region.
Consists of one or histogen theory peripheral layer of cells. So the apical cell theory was later superseded by histogen theory.
Hanstein in put forward histogen theory histogen histogen theory tissue builder. According to this theory the tissues of a plant body originate from a mass of meristem where the following three histogens can be distinguished Fig.
In Greek meaning skin.