Obviously being a bit obtuse. 19d Additives at that time included a gas (6). I have ethane - e (numbers)=additives, at that time = 'then' included a gas = 'a' therefore 'ethane'.
26a Tribunal has to obtain English food (9). I have 'courgette' - tribunal = court with to obtain = 'get' - English = 'e'.
If my solutions are correct it means courgette ends with an 'a'.
Please help.