In fact, a more appropriate view of this structure would re-direct attention from the sequence of passes to the central shared representation. When you declare that the tree is the locus of compilation information and the passes define operations on the tree, it becomes natural to re-draw the architecture as in Figure 18. Now the connections between passes denote control flow, which is a more accurate depiction; the rather stronger connections between the passes and the tree/symbol table structure denote data access and manipulation. In this fashion, the architecture has become a repository, and that is indeed a more appropriate way to think about a compiler of this class.
Happily, this new view also accommodates various tools that operate on the internal representation rather than the textual form of a program; these include syntax-directed editors and various analysis tools.