## 2 Results and Discussion
### Discrimination of Different Flower Stages by Electronic Nose
Volatiles with high positive scores on PC 2 include benzyl benzoate, methyl benzoate, (\(S\))-\(\alpha\)-methoxybenzeneacetic acid, nervl acetate, geraniol acetate, \(\beta\)-pinene, \(\beta\)-cubebene, (\(Z\),\(E\))-\(\alpha\)-farnesene, and l-alloaromadendrene, which are negatively correlated with the wilted-flower stage. The remaining 77 volatiles components, which include common components, \(\alpha\)-cubebene, bicyclogermacrene, \(\beta\)-gurjurene, and copaene, as well as relatively rare volatile compounds, including 3-hexen-1-ol, \(\beta\)-myrrene, \(\alpha\)-ylangene, do not exhibit any association with the first three components. As for the bud stage, 28 volatile compounds belonging to different chemical classes were identified: hydrocarbons (80.01%), esters (1.76%), aldehydes (3.18%), and alcohols (2.27%). The most abundant compound was \(\beta\)-caryophyllene, accounting for about 35% of the total GC peak area, followed by \(\alpha\)-caryophyllene (13.98%), D-germacrene (10.86%), (\(Z\),\(E\))-\(\alpha\)-farnesene (5.14%), and \(\alpha\)-ylangene (4.09%). With respect to other flower stages, the bud stage was characterized by higher hydrocarbons. As for the display-petal stage, 26 volatile compounds belonging to different chemical classes were identified: hydrocarbons (79.40%), esters (2.64%), alcohols (4.12%), and aldehydes (2.75%). The most abundant compound was \(\beta\)-caryophyllene, accounting for about 32% of the total GC peak area,  
Figure 4: Principal components analysis biplot showing relationship between the different stages of _C. odorata_ flower development and the volatile compounds: PC1 _vs._ PC2 plots **(a)** and PC 1 _vs._ PC 3 plots **(b)**. (I) bud stage, (II) display-petal stage, (III) initial-flowering stage, (IV) full-flowering stage, (V) end-flowering stage, (VI) wilted-flower stage, and (VII) dried flower stage. Black dots represent distribution of 92 volatile compounds in _C. odorata_ flower (numbers correspond to those in Table 1). followed by d-germacrene (13.73%), \(\alpha\)-caryophyllene (12.97%), \(\beta\)-cubebene (7.14%), and \(\alpha\)-copaene (6.02%). With respect to other flower stages, the display-petal stage was characterized by higher alcohols. As for the initial-flowering stage, 28 volatile compounds belonging to different chemical classes were identified: hydrocarbons (71.78%), esters (10.59%), acids (6.63%), alcohols (0.77%), and aldehydes (1.96%). The most abundant compound was \(\beta\)-caryophyllene, accounting for about 26.87% of the total GC peak area, followed by \(\alpha\)-farnesene (11.86%), \(\alpha\)-caryophyllene (10.19%), neryl acetate (7.89%), \(\beta\)-cubebene (7.35%), and d-germacrene (7.02%). With respect to other flower stages, the initial-flowering stage was characterized by higher acids. As for the full-flowering stage, 51 volatile compounds belonging to different chemical classes were identified: hydrocarbons (66.17%), esters (17.62%), acides (11.72%), aldehydes (3.83%), and alcohols (1.02%). The most abundant compound was \(\beta\)-caryophyllene, accounting for about 17.03% of the total GC peak area, followed by l-alloaromadendrene (12.79%), \(\beta\)-cubebene (11.79%), neryl acetate (11.74%), (\(S\))-\(\alpha\)-methoxybenzeneacetic acid (11.71%), and (\(Z\),\(E\))-\(\alpha\)-farnesene (6.91%). With respect to other flower stages, the full-flowering stage was characterized by higher esters and acids. As for the end-flowering stage, 40 volatile compounds belonging to different chemical classes were identified: hydrocarbons (51.07%), esters (26.38%), alcohols (1.13%), and aldehydes (2.87%). The most abundant compound was \(\beta\)-caryophyllene, accounting for about 15.05% of the total GC peak area, followed by geraniol acetate (13.78%), \(\beta\)-cubebene (12.91%), \(\beta\)-pinene (6.87%), benzyl benzoate (6.15%), and \(\alpha\)-farnesene (5.94%). With respect to other flower stages, the end-flowering stage was characterized by higher esters.