=head2 get_organism_by_species, set_organism_by_species

  Usage: my $species = $sample->get_organism_by_species();
         $sample->set_organism_by_species($species);

  Desc: get or set a organism_id in a sample object using species

  Ret:  get=> $species, a scalar.
        set=> none

  Args: get=> none
        set=> $species, a scalar

  Side_Effects: die if the argument supplied is not into the db

  Example: my $species = $sample->get_organism_by_species();
           $sample->set_organism_by_species('Solanum lycopersicum');

=cut


Concise version:
------------------------------------

=head2 (get/set)_organism_by_species

    my $species = $sample->get_organism_by_species();
    $sample->set_organism_by_species('Solanum lycopersicum');

Gets/sets a string organism name.  Dies if the given organism is not in the db.

=cut