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Perlite  [ Horticulture  ]

Dictionary of botanic terminology - index of names

     
  A volcanic mineral heated to make it expand. This reduces its density and helps increase porosity when added to potting soil.  
     
Perlite is an inert material derived from a naturally occurring volcanic rock, which when expanded by a heating process, forms white, lightweight granules. Perlite is a good soil amendment added to container potting mixes or other growing medium, to promote moisture retention while allowing good drainage. It is also useful to introduce air pockets in the soil enhancing aeration as well as to keep the soil from compacting. Perlite is chemically a sodium potassium aluminum silicate. Its size ranges, but it is about as large as gravel. See also vermiculite.
     

 


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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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