An occasional GC with an ill-defined border was invariably surrounded by a broad mantle zone ; those with indistinct mantle zones had well-defined , regular borders .
an occasional gc with an ill-defined border was invariably surrounded by a broad mantle zone ; those with indistinct mantle zones had well-defined , regular borders .
O O B-tissue O O O O O O O O O O O O O O O B-tissue I-tissue I-tissue O O O O O O