The simple answer is, those are nodes. If you were to cut a piece of the plant off containing a node, and stick it in a glass of water, the new roots would emerge from those nodes.

Omg thank you so much for clarifying that! I was so afraid it was something else.

You're welcome!

Marcy's exactly right, that's where the new growth comes from.

Just like this.

Perfect example Karen!

The nodes are where these things occur, where a leaf petiole attaches to stem. The bumps are aerial roots. Not all nodes have aerial roots.