Tag: botany

The histogen theory was given by Hanstein (1870). 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. A fourth histogen, the calyptrogen, produces the root cap.    
Thus, the correct answer is option A.    

• Promeristem is a group of young meristematic cells in its early embryonic stage from which other meristems are derived. 
  
• Apical meristems are derived from promeristem and are present below the promeristem at shoot tip and root tip.
  
• The shoot apical meristem (SAM) consists of three distinct meristematic zones called the histogens.
  
• These histogens are present at the growing tips of a stem or a root.
• These tips consist of three histogens and each of these histogens gives rise to tissues which are different from one another- dermatogen, periblem, plerome (principle tissues)
• The dermatogen or the outer layer gives rise to the epidermis, periblem or middle layer gives rise to the cortex as well as the epidermis, plerome or the inner layer gives rise to vascular tissues.
• So, the correct answer is 'Promeristem derivative destined to produce specific areas'.

Promeristem is the area of new development in a plant body where the establishment of new organs or parts of organs is started. Some of the time, it is additionally called primordial meristem, meristem and embryonic meristem.

• The quiescent centre is that part of the root-promeristems that contains the initials of epidermis, cortex and stele.
  
• These cells divide less frequently as they are inactive and are present at the pole of cortex and stele.
  
• The cells with QC have small dictyosomes, nuclei and nucleoli with little cytoplasm.
  
• These cells also have little endoplasmic reticulum, mitochondria and contain low concentrations of RNA, DNA and protein than the other cells of the root apex.
  
• So, the correct answer is 'Light cytoplasm and small nuclei'.

• The shoot apical meristem (SAM) form three distinct meristematic zones called the histogens.
  
• These histogens are present at the growing tips of a stem or a root.
  
• These tips consist of three histogens based on the type of cells they form.
• Each of these histogens gives rise to tissues which are different from one another- dermatogen, periblem, plerome (principle tissues)
  
• The dermatogen or the outer layer gives rise to the epidermis, periblem or middle layer gives rise to the cortex as well as the endodermis, plerome or the inner layer gives rise to vascular tissues.
  
• This is called histogen theory which was proposed by Hanstein in 1870.
  
• So, the correct answer is 'Type of cells they form'

The histogen theory was given by Hanstein (1870), According to this, there are 3 groups of initials in the shoot apex. According to Hanstein, 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. A fourth histogen, the calyptrogen produces the root cap.
Therefore, the correct answer is option C.  

• The Tunica-corpus theory explains the planes of cell division in the shoot apex.
  
• It was proposed by Schmidt in 1924.
• It was proposed on the basis of the study of shoot apex.
• This theory is applicable only to shoot apex and not to root. 
  
• This theory divides the region (shoot apex) into two tissue zones known as tunica and corpus.
• The shoot apex is composed of two layers of cells of tunica and corpus  (layer L1, L2 and L3 to denote the outer layer of tunica, the inner layer of tunica and corpus respectively).
• The plasmodesmata connections exist between the cells of tunica and corpus.
• So, the correct answer is 'Shoot apex'