Test	Leaves	Stem	Roots
N	25	25	25
Shapiro–Wilk W	0.2256	0.4168	0.4686
p(normal)	1.76 × 10−7	6.21 × 10−6	1.86 × 10−5
p (Monte Carlo)	0.0001	0.0002	0.0001
Conclusion: the three distribution are not Gaussian (normal). We must use a non-parametric test.