I’m using TikZ to draw linguistic syntax trees where some nodes have textual labels and some nodes don’t. I’d like the branch from a labelless node to continue at the same angle into the right hand daughter (or alternatively into the left hand daughter) as the branch that went to the node, so that the two branches form a visually continuous line at the same angle. I worked out how to do so for one labelless node using a kluge of lots of anchor specifications for each child. This fails to work for more than one labelless node and it’s a really messy method anyway. There must be a better way to do this but I haven’t figured it out. Any suggestions? (I’m using XeTeX but this shouldn’t matter I think.)
\begin{tikzpicture}[level distance=2em,
sibling distance=4em,
parent anchor=south,
child anchor=north,
anchor=north,
align=center,
% every node/.style={draw}
]
\node{DP}
child {node {Qfr}}
child {node (dbar) {}
child[parent anchor=north, anchor=base] {node {D}}
child[parent anchor=north, anchor=base] {node {ΦP}
child[parent anchor=south, anchor=north] {node {CP}}
child[parent anchor=south, anchor=north] {node (phibar) {}
child[parent anchor=north, anchor=base] {node {Nml}}
child[parent anchor=north, anchor=south] {node (phibar2) {}
child[parent anchor=north, anchor=base] {node {Φ}}
child[parent anchor=north, anchor=base] {node {NP}}}}}};
\end{tikzpicture}