94 INTRODUCTION 



the odour of orange-flowers, which also occurs in the flowers of species of Citrus, 

 and in a few species of Magnolia. The citron-odour of Thymus citriodorus, 

 Th. montanus and Dictamnus is due to citron-oil contained in the flowers, that of 

 Lavendula to the oil of lavender. 



Kerner's classification of odours is a very praiseworthy constructive eflfort, as 

 here, for the first time, grouping has been attempted on a scientific foundation, 

 according to the chemical composition of the odoriferous substances. That it is 

 only an attempt Kerner himself emphasizes. There is great difficulty in determining 

 the odours of flowers, more especially because it is largely a subjective matter : 

 as Kerner remarks one observer thinks he recognizes the odour of vanilla where 

 another perceives that of the violet. Both may be right, because, as a matter of 

 fact, two kinds of odour may simultaneously emanate from the same flower. But 

 it must be added that the sense of smell is very liable to be deceived ; while taste and 

 sight may both be concerned with such illusion (Kerner, op. cit., p. 203). When we 

 see a carnation, the odour of carnations at once comes to mind. This m.ay happen 

 before the odour proceeding from the carnation reaches the organs of smell. It is 

 therefore recommended that in determining an odour the flower should not be looked 

 at at all, the investigation being made with closed eyes. 



Odours agreeable to bees, lepidoptera, and hover-flies are also, as a rule, 

 acceptable to man, while many (e.g. indoloid and aminoid odours) which are 

 pleasing to flies are disagreeable to human beings. Carrion-flies and dung-flies 

 in particular (Sarcophaga, Calliphora, Scatophaga, Lucilia, and others) take pleasure 

 even in odours that are disgusting to us, licking and probing products of decom- 

 position (dunghills, decomposing flesh, liquid manure, pus, carrion) the colour and 

 smell of which fill us with loathing. There are also certain small flies and gnats, espe- 

 cially moth-flies (Psychodidae), which are everywhere common in closets, and delight 

 in the above-named disgusting substances. All these insects prefer to visit flowers 

 possessing odours or colours repulsive to us, and which have therefore already been 

 described (see p. 67) as Nauseous Flowers. Kerner (op. cit., p. 206) also advances 

 the view that many odours which are not perceived by man, are perceptible to 

 certain insects. As already mentioned (see p. 87), Kerner explains the regular visits 

 of Andrena florea to the small greenish flowers of Bryonia dioica, which, though 

 half hidden among fohage, it knows how to find, by supposing the existence of an 

 odour which is only perceived by this particular bee. The flowers are practically 

 odourless to human beings. The inconspicuous green flowers of Ampelopsis quin- 

 quefolia, scentless to us, are visited by bees, according to Kerner, with great 

 eagerness and industry. These insects may be seen flying to the plant from all 

 sides in a way leaving no doubt that its flowers are recognized at a considerable 

 distance. ' As it is not sight, it must certainly be the smell that leads to this 

 recognition. The flowers are odourless to human beings.' Kerner (op. cit.) gives 

 the following additional examples of inconspicuous flowers, which, though apparently 

 scentless to man and many animals, are eagerly sought out by particular insects 

 Aristolochia Clematitis, Vaccinium Myrtillus, Chamaeorchis alpina, and Listera 

 ovata. Kerner also thinks that the characteristic odour of many brightly coloured 

 flowers explains the constancy with which certain insects visit the same species 

 more or less exclusively. According to Kerner's view the odours of such flowers 



