Signal

Signal turns ordinary Houdini geometry, such as curves or a mesh, into an input the growth graph can read while the tree grows. It is for growth that responds to its surroundings: steering towards a target, keeping clear of an object, or reading a field.

The usual place for one is a Wrangle. Geometry wired into a Wrangle's third or fourth input is wrapped in a Signal for you, and your snippet reads it as VEX input 2 or 3. A Signal you place yourself is left as it is, which lets you set its name. The Signal tool on the Natsura toolbar is under Advanced.

name, its one setting, is the name the signal goes by. It defaults to the node's name; give each Signal its own name when you use more than one.

For effects built in, such as attraction to a shape or avoiding the tree's own branches, see Effectors first.