THE ANGIOSPERMAE 1267 



amine, which, when concentrated, creates "an ancient and fish-hke smell". 

 The same scent, with modifications due to admixture with other materials, 

 is repeated in many Rosaceae, and some Cornaceae and CaprifoHaceae 

 {Sambiiciis racemosa). Aromatic alcohols form a third group of distinctive 

 perfumes, such as eugenol (oil of cloves) in Dianthiis and cinnamyl alcohol in 

 Hxacinthus, and the group includes many other well-known scents, e.g., 

 Heliotrupiiim/Jasminum, Reseda, Convallaria, Lonicera and Viola, all delight- 

 ful to our senses. The distribution of these perfumes follows no systematic 

 grouping. The same or closely similar scents are to be found in flowers that 

 have no systematic affinity and, on the other hand, different species of one 

 genus may produce quite distinct perfumes; for example, Sambucus race- 

 mosa has a hawthorn scent, 5. ebidus a vanilla scent, and S. nigra a paraffi- 

 noid scent. Acids and alcohols derived from paraffins form a different group 

 of odours from those containing a benzene ring. To this group belong the 

 perfumes of Valeriana, Rosa, Riita, Tilia, Phlox and many Umbelliferae and 

 Cruciferae. To this group also belongs the honey-scent which is so com- 

 mon, for example in Trifoliiim. The last group of perfumes are those belong- 

 ing to the terpenes, such as oil of neroli in Citrus, oil of lavender in Lavandula 

 and oil of citron in Thymus, Verbena, etc. They are almost always produced 

 in internal glandular cavities. 



We have already mentioned the production of perfume only after dusk 

 by flowers pollinated by night-flying insects. The opposite event also 

 occurs, some flowers which are day-pollinated giving out perfume only 

 during daylight, when bees are flying, and becoming scentless at night. 

 Such are Spartiiim jimceum, Parnassia paliistris and some species of Tri- 

 folium and Daphne. 



Besides the insect visitors which are valuable as pollinators, flowers get 

 many " unbidden guests ", insects of either the wrong shape or the wrong 

 size to be satisfactory pollinators. There are a number of structural pecu- 

 Harities which have the effect of discouraging these intruders, or at least 

 the little ones. First the stems or the pedicels, or both, may be sticky, 

 usuafly from numbers of glandular hairs, which prevent creeping insects 

 from reaching the flowers. This may also extend to the calyx and in Cuphea 

 (Fig. 1209) the protection is limited to a barrier of sticky hairs on the ends 

 of the sepals, around the entrance to the flower. Against flying insects of 

 small size there are often internal barriers, most frequently of hairs, either 

 on the inside of the corolla, on the stamen filaments or along the style. Some- 

 times the protection takes the form of narrowing the channel to the nectar 

 by contraction of the floral tube, or by the inroUing of some parts of the 

 flower, in such a manner that only the proboscis of a large insect can pene- 

 trate it. In C^n^rfl;///;//^ r»^er both methods are combined (Fig. 1210). The 

 tube of the flower is divided longitudinally and only one of these channels 

 leads to the spur where the nectar is held. It is lined with hairs, while 

 the other channel, which leads to the ovary, has none. 



