## 3 Discussion  
Volatiles vary from plant to plant, and these changes are closely related to the structures of the flower organs [41]. Some researchers have found aromatic glands or osmophores inside the petals and other floral organs of the plants, which release special fragrances through diffusion [42]. This kind of aromatic gland usually has secretive tissue with thick layers of cells or presents as a droplet shape inside the cells and stores substances for short time periods [43; 44]. In this study, it was found that the petal surfaces of _N. hybrid_ were pleated and papillary, and the epidermal cells contained starches and osmophilic matrix particles in the flowering period. The petals of _N. hybrid_ have aromatic glands, and the parenchyma cells under the epidermis of the petals can form aromatic essential oils and temporarily gather aromatic oil substances, which can overflow through the fold structure of the epidermis cells and mastoid protrusions and release the fragrances of _N. hybrid._ [PERSON] et al. [45] studied the corolla structure and volatile substances of _Jasmin japonicum_ and found that the glandular hairs and 8-9 layers of parenchyma cells in the petals formed the structural basis for the specific production of floral fragrance. These folds, papillary, and other diverse secretory epidermal cells on the petals of _N. hybrid_ give the scent glands a large contact area with air, which is conducive to the release of volatile substances. By comparing the morphologies and ultrastructure of the petals in different strains of _N. hybrid_, it was found that the numbers and morphologies of papillae on the epidermis and the plastids, and osmophilic matrix particles in epidermal cells were different. It was speculated that the osmophilic matrix particles in the petals of _N. hybrid_ had certain relationships with the formation of fragrances and provided the material basis for the release of fragrance. According to the previous studies, plastids with plastoglobulin are the main organelles responsible for the production of terpen, esters, aldehydes, and alcohols [46; 47]. In this study, among the different flowers, the degree and density of the mastoid protrusions, the plastids and osmophilic matrix particles in the petals of the yellow _N. hybrid_ were higher than those of other strains; such anatomic structures may be the main reason for the higher content of esters and aldehydes in the yellow flower, which makes its aromatic substances more abundant and causes the release of higher quantities. [PERSON] et al. [48] confirmed that osmiophilic matrix particles played a key role in floral formation in a study of _Osmanthus fragrans_. Figure 7: Principal component analysis (PCA) of 12 samples based on PC1 and PC2 scores. V1–V64 represented the volatile substances numbered 1–64 in Table 1. (**A**) Loading plot of samples and the 64 volatile compounds; (**B**) loading plot of samples and the seven different classes of volatile compounds. HS-SPME-GC-MS provides a simple, rapid, and reliable technique for analyzing the volatile compounds in plants [49; 50; 51]. The volatile compounds of many water lily cultivars have been widely studied, and the volatile components differ [29; 52]. [PERSON] et al. [53] analyzed the components of essential oils from fresh flowers of the tropical water lily, and 25, 23, and 25 volatile substances were detected in the volatile oils of tropical \(N\). 'Ruby', \(N\). 'Daubeniana' and \(N\). _aearuela_, respectively. The main volatile substances were alkynes, alkanes, alkenes, alcohols, and ketones, among which 8-hexadecyne exhibited the highest content. In our study, 64 volatile compounds were detected and identified in the flower petals of four strains of \(N\). _hybrid_, including seven alcohols, six esters, seven aldehydes, six ketones, 13 alkanes, 22 alkenes and three others. In total, 29, 34, 39, and 43 volatile compounds were detected in Nh-1, Nh-2, Nh-3, and Nh-4.