[Alisdair]

What we are still missing, to complete the detective story, is an emblematic link between the saint and his balsam staff. He was very active during a bubonic plague episode but so far as I know this plant never became known as a protector from the plague.

[David Bracey]

The staff could be simply representative after all balsam is hardly strong enough to make a staff.  I will see what I have.

[Cali]

Knowing more about language than botany, I would venture that the word "balsam", or its variations in other languages but usually meaning "balm" (the same word probably) has been used to describe a variety of plants. Here in Corfu, for example, the name βάλσαμο (Balsamo, in case our forum doesn't do Greek) is used for a variety of spearmint, known in english as "Eau de Cologne"mint. (It invaded my annual bed a few years ago and practically evicted the lawful occupants.) What I'm getting at, if I haven't succeeded in confusing the issue,  is that the artist used the Balsam as symbolic of all medicinal balms.

[Alisdair]

Cali, That sounds the right track. And the soothing or calming quality of balsam would fit well with his work for orphans.