Which of the following plants does not have $Rhizobium$-containing root nodules?

$A$: Bacteria enter only the polyploid cells of the root cortex.
$R$: These cells provide cytokinins to bacteria,which promote bacterial cell division.

Which bacteria live symbiotically on the root system of leguminous plants?

Which of the following is responsible for nitrogen fixation in an aquatic fern?

Which of the following is a symbiotic nitrogen fixer?

The bacteria found in the root nodules of the family $Leguminosae$ are: