Figure 3. Evidence that Penstemon digitalis floral nectar is scented with (S)-(+)-linalool. Upper panel shows GC traces from SPME trapping of volatiles emitted by 35% sucrose solution on filter paper, either after 1 h incubation in the nectar tube of P. digitalis (upper trace) or from control filter papers (lower trace). The arrow indicates (S)-(+)-linalool, verified by MS and retention index on polar GC column using an authentic standard. Lower panel compares EI-quadrupole mass spectra from sucrose control (upper box) vs. flower-incubated sucrose (lower box), at the retention time (13.47 min) of (S)-(+)-linalool. The incubation of sucrose within the flower effectively reproduces the process of passive but selective absorption of polar volatiles by nectar in the corolla tubes of P. digitalis flowers.