American parent takes in empty laboratory where they're keeping the growths (6)
I believe the answer is:
polyps
'the growths' is the definition.
(polyp is a kind of growth)
'american parent takes in empty laboratory' is the wordplay.
'american parent' becomes 'pops' (I am not sure about this - if you are sure you should believe this answer much more).
'takes in' means one lot of letters goes inside another.
'empty' says to hollow out the word (remove centre letters).
'laboratory' with its centre removed is 'ly'.
'pops' placed around 'ly' is 'POLYPS'.
'where they're keeping' is the link.
This may not be right. Some or all of it may be part of another bit of the clue.
Can you help me to learn more?
(Other definitions for polyps that I've seen before include "sea anemone forms" , "Small growths on mucous membrane as in nose" , "Such as sea anemones" , "Organisms of which coral is composed" .)