Protected by sheets of glass, is raising flowers (7)
I believe the answer is:
pansies
'flowers' is the definition.
(I've seen this in another clue)
'protected by sheets of glass is raising' is the wordplay.
'protected by' means one lot of letters goes inside another (inserted letters are held or protected).
'sheets of glass' becomes 'panes' (I've seen this in another clue).
'raising' shows that the letters should be reversed in order (in a down clue, letters go up).
'is' written backwards gives 'si'.
'panes' enclosing 'si' is 'PANSIES'.
(Other definitions for pansies that I've seen before include "Flowers with velvety petals" , "Violas" .)