## 2 Results and Discussion
### Discrimination of Different Flower Stages by Electronic Nose
\begin{table}
\begin{tabular}{c c c c c c c c c c} \hline \hline \multirow{2}{*}{**Peak**} & \multicolumn{2}{c}{\(RT\)*} & \multirow{2}{*}{**Compounds**} & \multicolumn{6}{c}{**Relative Content (\%) \(\pm\) SD**} \\ \cline{3-10}  & \multicolumn{2}{c}{**(min.)**} & \multicolumn{1}{c}{**LRf *} & \multirow{2}{*}{**Compounds**} & **1** & **II** & **III** & **IV** & **V** & **IV** & **VII** \\ \hline
85 & 15.479 & 1237 & citral \(b\) & - & - & 0.202 \(\pm\) 0.000 & - & 0.059 \(\pm\) 0.006 & - & 0.538 \(\pm\) 0.000 \\
86 & 15.486 & 1239 & \(\beta\)-citral & 0.623 \(\pm\) 0.111 & 0.512 \(\pm\) 0.512 & - & 0.194 \(\pm\) 0.086 & - & - & 0.081 \(\pm\) 0.025 \\
87 & 16.322 & 1268 & \(a\)-citral & 2.226 \(\pm\) 0.269 & 2.166 \(\pm\) 0.221 & 1.756 \(\pm\) 0.085 & 1.685 \(\pm\) 0.314 & 1.377 \(\pm\) 0.046 & 1.021 \(\pm\) 0.093 \\
88 & 27.365 & 1709 & faresal & - & - & - & - & 1.128 \(\pm\) 0.014 & - \\
89 & 27.965 & 1736 & (\(E\),\(E\))-faresal & 0.192 \(\pm\) 0.014 & - & - & 0.034 \(\pm\) 0.023 & - & 3.131 \(\pm\) 1.136 & - \\ \hline \multicolumn{10}{c}{**Kotones**} \\ \hline
90 & 7.892 & 981 & methyl heptone & - & - & - & - & - & 0.218 \(\pm\) 0.013 \\
91 & 14.153 & 1192 & 2-hydroxy-3-cyanopyridine & - & - & - & 0.047 \(\pm\) 0.001 & 0.101 \(\pm\) 0.055 & - & 0.089 \(\pm\) 0.007 \\
92 & 25.197 & 1613 & juneal & - & - & - & - & - & 0.665 \(\pm\) 0.000 \\ \hline \multicolumn{10}{c}{* \(RT\) = Retention time (minately; * _LRf *_Linear retention indices to C\({}_{7}\)-C\({}_{8}\) n-classo on DB-5 MS column, _LRf_ increases were according to the results of _[PERSON] et al._[2], the database of _PCY_ 15.1, and the _Phochimica_.} \\ \hline \hline \end{tabular}
\end{table} 
Table 1: _Cont._
Variations of the volatile compositions emitted by _C. odorata_ flowers significantly depend on the stage of maturity. The same phenomena are also observed in other plant species, such as _Michelia alba_[21], and _Michelia champaca_ flowers [16]. In this study, the highest floral volatile polymorphism was detected at the intermediate levels of flower development, and the richness of volatile compounds showed a \begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline  & **I** & **II** & **III** & **IV** & **V** & **VI** & **VII** \\ \hline I & 100 & & & & & & \\ II & 77.34 & 100 & & & & & \\ III & 58.37 & 66.78 & 100 & & & & \\ IV & 41.61 & 41.90 & 59.68 & 100 & & & \\ V & 32.84 & 42.16 & 52.26 & 50.98 & 100 & & \\ VI & 54.90 & 60.00 & 61.08 & 35.02 & 41.49 & 100 & \\ VII & 59.99 & 65.60 & 61.02 & 42.63 & 42.33 & 53.44 & 100 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: The Bray-Curtis similarity values (%) among different stages of _C. odorata_ flower development. (I) bud stage; (II) display-petal stage; (III) initial-flowering stage; (IV) full-flowering stage; (V) end-flowering stage; (VI) wited-flower stage; and (VII) dried flower stage. Figure 3: The composition of volatile compounds in different stages of _C. odorata_ flower development by HS-SPME-GC-MS. **(I)** bud stage; **(II)** display-petal stage; **(III)** initial-flowering stage; **(IV)** full-flowering stage; **(V)** end-flowering stage; **(VI)** wited-flower stage; and **(VII)** dried flower stage. unimodal or hump-shaped pattern between the number of VOCs and times of flower development. To identify which volatiles contributed the most to the differences among the seven flower stages, the data on 92 volatile compounds identified in _C. odorata_ at a full life-flower scale were analyzed by using principal component analysis (PCA). The first three components of PCA explained 73.87%, 10.58%, and 7.05% of the variation, explaining \(\sim\)92% of combined variance (Figure 4). Hereinto, volatiles that had high positive scores on PC 1 include \(\alpha\)-caryophyllene, D-germacrene, \(\alpha\)-farmesene, \(\delta\)-cadinene, \(\alpha\)-citral, and \(\beta\)-caryophyllene, which are highly positively related to the bud, display-petal, and initial-flowering stages.