  Infinitely many large Schur sigma-groups G with non-elementary bicyclic
commutator quotient G/G' = C(3^e) x C(3), e >= 2, are constructed as periodic
sequences of vertices in descendant trees of finite 3-groups. A single root
gives rise to pairs of metabelian groups G with logarithmic order lo(G) = 4+e
for e >= 3. Three roots are ancestors of pairs of non-metabelian groups G with
moderate rank distribution rho(G) = (2,2,3;3) and lo(G) = 7+e for e >= 5.
Twentyseven roots produce sextets of non-metabelian groups G with elevated rank
distribution rho(G) = (3,3,3;3) and lo(G) = 19+e for e >= 9. The soluble length
of non-metabelian groups is always sl(G) = 3. The groups can be realized as
3-class field tower groups Gal(F(3,infty,K)/K) of imaginary quadratic number
fields K = Q(d^1/2) with fundamental discriminants d < 0.
