Why probably?  This is a good example of how difficult it is to be sure.  It could be a New England Glass Company Poinsettia. 

You could argue the case either way:

• Lutz Rose center:   Always associated with Boston & Sandwich 
• Leaves:   Sandwich type, NEGC leaves are different 
• Latticinio: Almost always NEGC.  There are very few examples (if any) of Sandwich weights which use latticinio
• Flower petals:  Could be labeled either way, but some writers say the shape of the petals and the arrangement is NEGC

Two good references on this subject are:

• Kulles "Identifying Antique Paperweights - Lampwork"
• Hawley "The Art of the Paperweight  - The Boston & Sandwich and New England Glass Companies"

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