OIL SECEETIOXS. 325 



" The conclusions to be drawn from these researches are : — 



u-^Q — j^i^Q^i the essential oil is generally found localised in the 

 epidermal cells in the upper surface of the sepals or petals, though 

 it may exist upon both surfaces, especially if the floral organs are 

 completely hidden in the bud. The lower surface generally 

 contains tannin or pigments derived from it. 



" 2^ — The essential oil seems in all cases to be the result of a 

 transformation of the chlorophyll. This transformation is readily 

 understood if it be admitted, as it generally is, that the floral 

 organs are but leaves modified for the performance of a new 

 function. The chlorophyll being thus diverted from its original 

 purpose or use, is transformed into permanent tannoid compounds 

 or into essential oils. 



"3^ — The liberation or disengagement of perfume from the 

 flower only becomes perceptible when the essential oil is sufficiently 

 freed from the intermediate compounds which generated it. Its 

 formation is to some extent in inverse proportion to that of the 

 tannin and colouring matters in the flower. This will explain why 

 flowers with green petals possess no odour," — [This observation is 

 not quite correct ; the flowers of the vine, for instance, are green, 

 but they are strongly scented : their perfume approaches that of 

 the mignonette (as does the " ferment oil " of the leaves of the 

 vine, w"hich is suggestive). The flowers of Uvaria dulcis, Cananga 

 oclorata and Michclia Chcun]3aca are of a greenish-yellow in the 

 countries where they naturally grow, but w^hen grown in England 

 their flowers are of a sickly green colour, by reason of lack of 

 sunlight, but yet they are odoriferous.] — " and why white or pink 

 flowers are most frecjuently odoriferous;" — [It has been found that 

 the order of rotation in which perfumes are generated in flowers, 

 in respect to their colour, is as follows : — AVhite, Yellow, Eed, 

 Blue, Green, Orange, Brown.] — " why the Compositce are so rich in 

 tannin,* and why the cultivated white lilac and forced roses 

 acquire a very fine perfume." — [This also is a weak inference. The 

 perfume of white lilac and white heliotrope can hardly be 

 considered finer than that produced from the same plants growing 

 in the free air and attaining their natural colours. Some perfumes 

 which are rank when produced from flowers grown in the open air 



* Eev. Gen. de Bot., ii., p. 391. 



