## 3 Functions of \(\beta\)-Ocimene in Flowers
Circadian rhythms that make floral scents follow diurnal or nocturnal periods of emission are adapted to match the periods of activity of the respective pollinators [32; 33; 34; 35; 36; 37; 38; 39]. Ontogenical changes in floral scent along flower lifespan may also occur because flowers modify or reduce their floral scent once they are pollinated to reduce the costs, to prevent visits by pollinators and other floral visitors that can have harmful effects on floral structures, and to direct pollinator visits to unpollinated flowers [37; 40; 41; 42]. There are several case studies demonstrating that \(\beta\)-ocimene emissions of different species show  
Figure 3: Ancestral phylogenetic reconstruction of floral emissions of _trans_-\(\beta\)-ocimene. One thousand trees were simulated with a mapped discrete character with states “Emitter” and “Non-emitter”. Trees had an average of 231.716 changes between states. The changes were: 117.436 Emitter\(\rightarrow\)Non-emitter and 114.28 Non-emitter\(\rightarrow\)Emitter. Mean times spent in each state were: 50.47% Emitter and 49.53% Non-emitter. patterns of emission similar to those mentioned. _Rannuculus acris_ flowers have a floral scent dominated by \(\beta\)-ocimene and its petals present emissions that differ quantitatively between the apical and basal regions, paralleling optical nectar-guide patterns that guide pollinators to the nectaries [31]. The flowers of _Mirahilis jalapa_ emit a floral scent that is strongly dominated by _trans_-\(\beta\)-ocimene, its main site of emission are the petaloid lobes located at the flower limb, and its emissions describe an evening maximum between 17:00 and 20:00 that matches nicely with the flower opening and the activity of its crepuscular hawkmoth pollinators [36]. The floral scent of snapdragon (_Antirrhinum majus_) is dominated by _trans_-\(\beta\)-ocimene, whose emission follows a diurnal cycle controlled by a circadian clock, with the highest emission rates between 11:00 and 18:00 [16]. [PERSON] et al. [16] showed that the rhythmic floral emission of _trans_-\(\beta\)-ocimene and other monoterpenes displayed a \"free-running\" cycle in the absence of environmental cues, with complete independence from light, indicating the circadian nature of its diurnal rhythmicity. The rates of emission of _trans_-\(\beta\)-ocimene from the flowers of snapdragon and Satsuma mandarin (_Citrus unsliu_) vary with floral ontogeny, with maximum emissions when flowers are fully open and mature and need to be pollinated, and decreasing emissions in later periods until fruit development [16; 43]. Such spatial and temporal patterns of emission indicate a clear involvement of \(\beta\)-ocimene in the attraction of pollinators to flowers in these species [30]. However, the effects of \(\beta\)-ocimene on pollinators may be dependent on the context, i.e., on whether it is presented within the correct blend of floral and whole plant volatiles [44], and also with the correct combination of floral and plant traits other than scent. Different patterns of emission are shown when floral volatiles develop biological functions other than pollinator attraction. For example, the emission of floral volatiles that serve as a defence against herbivores and florivores can be temporally induced after suffering an attack [45; 46]; but constitutive floral emissions of these compounds that might interfere with pollination and constitute an unnecessary cost for the plant are generally avoided by animal-pollinated flowers [30; 47; 48]. Also, some volatile and non-volatile secondary metabolites with antibacterial and antifungal properties that develop defence functions against microbial pathogens are abundant in flowers [49; 50]; they are constitutively produced and accumulated especially in floral tissues that the plant must protect even at a high cost because they are costly to produce, they are rich in nutrients, and they are important for plant reproduction, like for example nectar [51; 52; 53] and pollen [54; 55].