Possible Clues:

• This won't get you down seeing it's so poisonous
• Father becomes poisonous with us around
• 31 across, as a poison
• This won't get you down, as it's got poison in it
• Source of poison a saint used after appearing for trial
• Tree from Java with poisonous sap
• Tree yielding poisonous sap
• This won't get one down as it's so poisonous
• It could kill, though not down as a poison
• Not down in the way to get you right down