  Proximity effect and pair tunneling models are applied as alternative
scenarios to explain the recently measured $ab$-plane and $c$-axis components
of the superfluid tensor in Copper-Oxide superconductors which contain chains,
such as $YBa_2Cu_3O_{6.95}$. It is argued that conventional proximity effect
models, which couple chains and planes via single electron tunneling only, are
incompatible with the experimental observations. On the other hand several
surprising features of the experimental data are readily explained by the
presence of a microscopic pair tunneling process.
