Test	Leaves	Stem	Roots
N	25	25	25
Shapiro–Wilk W	0.2534	0.2153	0.4847
p(normal)	2.85 × 10−7	1.48 × 10−7	2.65 × 10−8
p (Monte Carlo)	0.0001	0.0001	0.0001
Conclusion: the three distribution are not Gaussian (normal). We must use a non-parametric test.