  For 25 orthogonal groups of signature $(2,n)$ related to the root lattices
$A_1$, $2A_1$, $3A_1$, $4A_1$, $A_2$, $A_3$, $A_4$, $A_5$, $A_6$, $A_7$, $D_4$,
$D_5$, $D_6$, $D_7$, $D_8$, $E_6$, $E_7$, we prove that the algebras of modular
forms on symmetric domains of type IV are freely generated by the additive
lifts of some special Jacobi forms. The proof is universal and elementary.
