The cluster grows outwards, growth inside the cluster is slow, since a wandering particle must avoid the branches in order to reach deep inside.

The simulations show that having a smaller stickiness coefficient makes for a smaller cluster, because it's easier for a wandering particle to penetrate deeper. The larger the stickiness coefficient the more the cluster branches out. It's also interesting to see the similarity of the patterns to natural phenomenon, suggesting that DLA model correctly captures the physics these phenomenon.