Tag: theories of shoot apical meristem development

A simple leaf can be differentiated from the pinnae of a compound leaf on the basis of the presence or absence of 'axillary bud'.

Actually there are generally three buds in the region of eye. Only one is axillary. The other two are accessory. 

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.    

 The formation of the root apex involves derivatives of both the basal and apical cells of the two-cell embryo, the hypophyseal region derived from the topmost cell of the suspensor is incorporated into the embryo proper, giving rise to part of the root cap.

• 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.