From the book:

The structure is again similar to proxy and object adapter. The difference is that there is a one-to-many relationship between the composite and the component. The client speaks to the top-level component class.

In both composite and proxy patterns, the client would use the top-level interfaces of Subject or Component. However, the composite pattern has a one-to-many relationship between its Composite and Component, whereas the proxy pattern has a one-to-one association between its Proxy and Subject.