## 2 Results
### Among-Organ Differences of VOC Emission  
The VOC emission (especially aliphatic alcohols and monoterenes) from the stamens of _L. caudata_ was greater than the other floral parts (28,653.62 ng/40 min) (Figure 5, Table S1). Thirty VOCs were identified from five isolated flower parts and were grouped by their biochemical synthesis pathways as shown in Table S1. Stamens released the most VOCs, reaching 20, followed by petals with 15. Flower pedicels emitted the fewest number of VOCs (4). The scent composition based on the relative amounts varied greatly within flowers (Figure 6). The stamen fragrance was characterized by high levels of aliphatic alcohols (44.43%) and monoterenes (44.61%), which were similar to the fragrance of the whole flower. Petals had relatively high amounts of benzenoid-alcohols (e.g., phenylethyl alcohol; 36.71%) and irregular terpen (e.g., \(p\)-anisaldehyde; 34.01%). The calyx aroma was relatively rich (59.11%) in aliphatic alcohols (e.g., leaf alcohol), whereas the pedicel mainly released benzenoid-esters (44.89%). Pistils also emitted compounds that originated from the three main biosynthesis pathways. Figure 5: Total emission amounts of VOCs emitted from _L. caudata_ flowers and their isolated floral parts. Figure 6: Venn analysis of VOCs identified from five floral organs in _L. caudata_. P1, stamen; P2, petal; P3, calyx; P4, pitstil; P5, pedicel. For the composition of scent, eight VOCs, mainly monoterpenes, were detected only in the stamens (isopulegol; lavandulol; r-cyclodextrinaniol; nerol; geraniol; 2-undecanol; 2-heptanol; and 2-nonanone). Four compounds (\(p\)-anisaldehyde, benzeneacetaldehyde, citronellal, and eicosane) were only emitted from petals. Lipoxygenase products or \"green leaf volatiles,\" such as _trans_-2-hexenal, leaf alcohol, _cis_-2-hexen-1-ol, and 1-hexanol, were mainly expressed specifically from the calves. Linalool was the only VOC that was released only from pistislis; it was not detected from pedicels. The daily emission patterns of 2-heptanol, nerol, and linalool were presumed to be closely related to the opening of flowers in _L. caudata_. These compounds are likely to act as cues to pollinators in _L. caudata_. Another six compounds had no obvious tissue specificity (mainly found in stamen and petal) (Figure 7). Difference Analysis of VOCs in Different Flower Parts and Flowering Stages Based on Bray--Curtis Dissimilarity Analysis and Principal Component Analysis  
The BrayCurtis dissimilarity index is often used to compare the degree of dissimilarity between two samples [18]. Larger values of the index suggest greater differences between samples (low similarity) [19]. The Bray--Curtis dissimilarity index across the three flower stages ranged from 0.6333 to 0.8611 (Table 3), which indicated that the floral release compounds changed considerably during the flowering time. For all identified compounds in the five floral organs, the index ranged from 0.4084 to 0.9943 (Table 4). The pistil and pedical showed some similarity (dissimilarity index 0.4084), whereas there were significant differences between other parts (dissimilarity indexes greater than 0.7608). \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Flowering Stage** & **T1** & **T2** & **T3** \\ \hline T1 & 0 & & \\ T2 & 0.8611 & 0 & \\ T3 & 0.6333 & 0.7271 & 0 \\ \hline \hline \end{tabular} Note: T1, pre-blooming stage; T2, full-blooming stage; T3, over-blooming stage.  
\end{table} 
Table 3: Bray–Curtis dissimilarity index among different flowering stages of _L. caudata_. Figure 7: Heat-map with volatiles identified from a single flower and its five floral organs in _L. caudata_. T2, single flower; P1, stamen; P2, petal; P3, calyx; P4, pistil; P5, pedicel. To identify compounds that contribute significantly to the variation in VOC profiles of five floral organs from _L. caudata_, a principal components analysis (PCA) was performed. Three components accounting for 78.80% of the total variance was extracted. PC1, PC2 and PC3 explained 42.90%, 23.50% and 12.40%, respectively (Table 5).