Botany Sem II/ Unit II Pteridophyta/Selaginella/Morphological Nature of Rhizophore

      Rhizophores are the colourless, aphyllous, elongated and cylindrical appendages which arise from each ramifications i.e.; dichotomy of the prostate leafy stem of Selaginella.             It develops exogenously from the special angle meristem present between the branches of the stem. When it touches the ground, it shows subapical growth with two meristematic zone each one with one root initial and turned into two roots which again form few adventitious roots.                                              There are 3 different viwes about the Morphological Nature of Rhizophores, which are as follows:.                                                                           (1) Capless Root Hypothesis : Harvey Gibson (1902) , Uphof (1920) ,Wochok and Sussex (1974) treated it as a root , because :                                  (a) It grows rapidly towards the soil , i.e.; positively geotropic.                             

 (b)It is aphyllous,i.e.; leafless.                    (c) Anatomically both of the rhizohore and root are same because:.            

           (i) Epidermis is unilayered.                 (ii) Cortex is divided into hypodermis,general cortex and one  layered endodermis.                                       (iii)The stele is small with a monarch ,exarch xylem.                                (d) A few species like S.densa,S.krausiana,S.martansii and S.wallachi etc possess root cap (Webster and Steeves,1967).                    (e) A Rhizophore can transport auxin acropetally as like as a root (Wochok and Sensex,1974).                                                                               Rhizohore is always monostelic even though the stems are polystelic. In stem , endodermis is modified to trabeculae but in rhizome and root it remains intact. So,a rhizohore is a root .                                                                                            (2) Leafless Shoot Hypothesis :                                                                   According to Bruchmann(1871) ,Worsdell(1910) a rhizohore is a aphyllous shoot , because :                          (A) In most of the species there is no root cap in rhizohore .                (B) It originates exogenously which is same in case of a stem also  .             

         (C) It develops from the angle meristem which is basically an embryonic shoot (Curick,1959).                 (D). They do not bear any absorbing root hair .                                    (E) Under experimental condition a rhizohore is transformed into a leafy-shoot (Foster and Gifford,1959).                       (F). The biochemistry of a rhizohore is close to the biochemistry of stem rather than a root.                                                                                                             Schoute (1938) opined that a rhizohore is a modified specialized stem in the direction of a root because roots appear from it when it touches the soil.                                                                                                        (3) Sui-generis Hypothesis :                                                                               Bower(1908,1938) and Gobel (1905) suggested that a rhizohore is neither a root nor a shoot,but an organ "Sui-generis" i.e.; having absolutely no parallel structure anywhere in the Plant Kingdom other than Selaginella itself. Thus, a rhizohore is altogether a new structure .