322 ODOEOGEAPHIA. 



judicious combination of others : the most difficult to imitate by a 

 blend of natural essences is the jasmin (if it can Ije imitated at all), 

 but yet the impression it makes on the olfactory nerve is not a 

 simple one, as in the case of Rosa centifolia, but it reminds in an 

 indescribable way of certain organic compounds occasionally 

 produced in the laboratory. 



The compound nature of the perfume of orange-blossom, which 

 has hitherto been considered to be a simple odour, has been proved 

 by the researches of Mesnaud (Eecherches sur le mode de produc- 

 tion du parfum dans les fleurs, Xote de E. Mesnard, presentee a 

 r Academic par Duchartre*). The investigation was conducted in 

 the Botanical Laboratory of the Sorbonne, under the direction of 

 Gaston Bonnier. Mesnard's interesting and suggestive memoir 

 may be abstracted as follows, the passing comments inserted 

 between brackets being my own : — 



"The imperfection of the micro-chemical methods usually 

 employed has hitherto prevented an exact knowledge being obtained 

 of the manner in which the perfume of flowers is generated (and 

 localised in the flower). In this particular investigation I have 

 followed the same method of research which was adopted in the 

 localisation of fixed oils. The method is as follows : — The section 

 being placed in a drop of pure glycerin is arranged upon a round 

 cover-glass, which being then inverted, serves as a cover to a small 

 chamber formed by cementing a glass ring to an object-slide. In 

 the interior of this chamber is fixed another ring of smaller 

 diameter, and somewhat less in height, thus forming an inner 

 annular space in which the reagent may be placed. By adopting 

 this arrangement the light passing through the central part of the 

 cell is not weakened. The inner ring further serves to support a 

 very small cover-glass upon which sections may be arranged 

 which require to be exposed to the action of the reagent for some 

 length of time, as occasionally happens in the case of fixed oils. 

 The reagent invariably employed is pure hydrochloric acid, the 

 hydrated acid vapors abundantly given off from which are absorbed 

 with avidity by the glycerin. In this way, by a gentle and easily 

 regulated action, I obtam complete hydration of sections in the 

 presence of an acid. After a few moments of exposure to the 

 presence of the reagent, the essential oils appear as minute 



* Comptes Rendus, 21st Nov., 1892, cxv., p. 282. 



