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The teacher passed on her knowledge to her students.
This ring has been passed down in my family for 300 years.

Could you dig up a reason why the first sample uses on while the second down in a similar construction? Thanks.
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down the family line/tree
Comments  
Students: Are you brave enough to let our tutors analyse your pronunciation?
Marius Hancudown the family line/tree
Thanks, Marius, for the reasonable reply to down the family line/tree.

But how should I justify pass on?
On indicates continuance
Thanks, Marius.

Got it.
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