Popular experiment begins in North-Eastern part of the alimentary canal (9)
I believe the answer is:
intestine
'part of the alimentary canal' is the definition.
(I know that intestine is part of gastrointestinal tract)
'popular experiment begins in north-eastern' is the wordplay.
'popular' becomes 'in' ('in' can mean trendy).
'experiment' becomes 'test' (test is a kind of experiment).
'begins' indicates taking the first letters.
'north eastern' becomes 'NE' (abbreviation).
The initial letter of 'in' is 'i'.
'in'+'test'+'i'+'ne'='INTESTINE'
(Other definitions for intestine that I've seen before include "Being gutted, one loses it" , "Part of the alimentary canal" , "Some guts" , "canal section" .)