By Rag
United Kingdom 
For some years now I have had a minature Orange tree that has produced plentiful crops of small oranges. This year, however, I also have lemons growing from branches on the same trunk as those branches with oranges. The lemons are close to being full size. Any explanations please?
24 May, 2014
It appears that the orange was grafted onto a Lemon rootstock and the branches that your lemons are on is coming off the rootstock portion of the tree.
Check that these branches with the lemons on are not below the graft. If they are then cut the branches off.
You could also leave these branches on and grow both oranges and lemons as a fruit cocktail tree.
24 May, 2014