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Pith  [ Botany ]
Adjective: Pithy
Synonym:
  Medulla (Adj: Medullar) 

Dictionary of botanic terminology
Index of names

     
  The pith or medulla is the spongy tissue forming the central cylinder of the stem of most flowering plant, especially those of the dicotyledonous. It consists of cellular tissue composed mainly of parenchyma.  
     


Cross section of a stem of Astrophytum myriostigma
The pith (Medulla) is the whitish spongy tissues encircled by the ring of vascular
bundles in the centre

Pith is a light substance originating from the ground meristem that is found in vascular plants, it is largely composed of spongy parenchyma tissue modified for storage, that has very little structural strength and is located in the centre of the stem of the Dicotyledons and in the non-woody roots of monocotyledon to the inside of the stele.  It is encircled by a ring of xylem (woody tissue), and outside that, a ring of phloem (bark tissue). In most plants the pith is solid, but some plants, e.g. grasses and umbellifers, the pith has a hollow centre forming a hollow tube except at the points where leaves are produced, where there is a solid plate across the stem. A few plants, e.g. walnut, have distinctive chambered pith with numerous short cavities in the pith.
The pith varies in diameter from about 0.5 mm to 6-8 mm in solid pith of woody plants, up to 30 mm in succulent stem of cacti or even 150 mm or more in the stems of some plants with hollow pith, e.g. some bamboos. Freshly grown pith in young new shoots is typically white or pale brown, commonly darkening with age.
In woody plants (trees, shrubs), the pith becomes surrounded by successive annual rings of wood -- it may be very inconspicuous but is always present at the centre of a trunk or branch.   Compare with: Cortex

 


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Holdfast roots  [ Botany  ]

Dictionary of botanic terminology - index of names

 
     
  Some species of climbing plants develop holdfast roots which help to support the vines on trees, walls, and rocks. By forcing their way into minute pores and crevices, they hold the plant firmly in place.  
     
Climbing plants, like the poison ivy (Toxicodendron radicans), Boston ivy (Parthenocissus tricuspidata), and trumpet creeper (Campsis radicans),  develop holdfast roots which help to support the vines on trees, walls, and rocks. By forcing their way into minute pores and crevices, they hold the plant firmly in place. Usually the Holdfast roots die at the end of the first season, but in some species they are perennial. In the tropics some of the large climbing plants have hold-fast roots by which they attach themselves, and long, cord-like roots that extend downward through the air and may lengthen and branch for several years until they strike the soil and become absorbent roots.

Major references and further lectures:
1) E. N. Transeau “General Botany” Discovery Publishing House, 1994
     

 

 

 

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