OIL SECEETIOXS. 323 



spherical drops of a fine transparent golden yellow. If the action 

 be prolonged, the drops disappear, being transformed into diffusible 

 products. The disappearance or diffusion of globules of fixed oils 

 never takes place, the process thus furnishes a means of dis- 

 tinguishing these two classes of products. 



" As regards the localisation of essential oils in the parts of the 

 flower, the following observations have been made: — 



" Jasmin. In this flower the oil is situated in the row of 

 epidermal cells on the upper side of the sepals and petals. Some 

 exist also in the corresponding layer on the under surface, where 

 the sepals are coloured by a violet pigment. If the evolution of 

 the cell-contents in flowers at different stages of development be 

 followed, at first nothing but chlorophyll is found in the tissue ; 

 tannin is the next to appear, or rather intermediate glucosides, 

 difficult to identify by means of the ordinary tests for these 

 substances. These glucosides furnish the tannin and pigments of 

 the lower surface of the sepals. The hydrochloric acid vapours 

 furnish a means of distinguishing all the tannoid compounds inter- 

 mediate between the chlorophyll and tannin, or pigments, on the 

 one hand, and between the chlorophyll and essential oil on the 

 other. The explanation of these facts seems to be as follows : — 

 Whereas, upon the lower surface, which, in the bud, was exposed 

 to the action of light and the oxygen of the air, the tannoid 

 compounds were slowly oxidised, thereby generating tannin, the 

 upper surface, on the contrary, being then hidden inside the bud, 

 these agencies were inoperative (the parts not being exposed to 

 the action of light and oxygen), and the same compounds were 

 converted into essential oil, which oxidises when in contact with 

 air, and so produces the sensation of perfume." — [This confirms 

 the theory of Liebig and others, that perfume is the result of 

 eremacausis.] 



''Rose. The essential oil of rose is found in the papilliform 

 epidermal cells on the upper surface of the petals, scarcely ever on 

 the lower side." — [Blondel states* that the otto is secreted in cells 

 on both its surfaces, those of the upper epidermis being of a 

 papillary form, and those of the lower of an elongated cubic form. 



* Produits odorants des Rosiers et Bull, de la Soc. Bot. de France, Feb., 

 J890. 



