sclereids

Plant Tissues: Ground

Ground Tissues consist primarily of thin-walled parenchyma cells. Other ground tissue is composed of collenchyma cells and sclerenchyma cells

parenchyma cells 

  • most common type of plant cell
  • large vacuoles, thin walls, and are initially(briefly) more or less spherical 
  • living protoplasts push up against each other shortly after being produced and produce other shapes, ending up with 11 to 17 sides. 
  • function in storage of food and water, photosynthesis, and secretion
  • most abundant cells of primary tissue and may also occur in a much lesser extent insecondary tissues. 
  • most only have primary walls(walls laid down while the cells are still maturing)
  • less specialized than other plant cells, although many variations occur with special functions ( nectar and resin secretion or storage of latex, proteins, and metabolic waste). 
  • functional nuclei and are capable of dividing
  • remain alive after maturation; (100 years old in cacti)
  • some contain chloroplasts (especially in leaves and other outer plant parts)- photosynthetic parenchyma tissue called chlorenchyma

collenchyma cells

  • have living protoplasts and may live for many years 
  • usually a little longer than wide
  • have walls that vary in thickness
  • provide support for plant organs, allowing them to bend without breaking(flexible) 
  • often form strands or continuous cylinders beneath the epidermis of stems or stalks and along the veins in leaves.
  • provide much support for stems in primary plant body.
  • example: celery strings.

sclerenchyma cells 

  • tough, thick walls. 
  • usually lack living protoplasts at maturity (unlike collenchyma and parenchyma)
  • secondary cell walls impregnated with lignin
  • lignin -highly branched polymer that makes cell walls more rigid. cell walls containing this are considered lignified. Common in walls of plant cells that have a structural or mechanical function. Could be in primary walls as well. 
  • two types: fibers and sclereids; both serve to strengthen the tissues in which they occur
  • fibers - long, slender cells that are usually grouped together in strands.
  • sclereids- variable in shape but often branched.May occur singly or in groups; they are not elongated, but may have many different forms (one is a star). Found in hard seed coats. Cause gritty texture of pair. 

BIOL 1105/1106 Virginia Polytechnic Institute and State University