How to make a volume filled with a cloud of instances of another object

Is it possible to use one object to define a boundary, the inside of which is filled to some specifiable level of density with a cloud of objects, these being instances of another object? For example, suppose I want to make something that looks like topiary, being composed of a dense mass of leaves, but having a clearly defined shape that I could sculpt. I don’t want the objects to simply populate a surface, like hair, but rather to fill the volume. Possible?

Never mind. I figured out how to do it using the particle system.