if it is like a little brown dome that you can 'pop' and goo comes out, it's a scale. an insect. sucking sap from the plant. they can be hard to get rid of and can spread quickly to other plants they like. any decent bug spray can help get rid of them, but manually wipe the visible ones away. they are the females, the males are microscopic i hear. i use water with some mild dishsoap (not caustic washing machine detergent) for bugspray. heavy infestations can be dipped in rubbing alcohol after cleaning them up and then potting in new bark.