CELL-CONTENTS AND FORMS OF CELLS. 235 



coriander, etc. Esters of benzoic and cinnamic acids are found 

 in storax, Tolu balsam, and Peru balsam. Bornyl isovalerate 

 occurs in valerian oil. 



LACTONES. The odoriferous principle known as coumarin is 

 widely distributed in the plant kingdom. It occurs in some of 

 the ferns, grasses, tonka bean, " Waklmeister " (Asperula 

 odorata), etc. It apparently is formed as the result of the action 

 of a ferment, as it is detected only after the drying of the plant. 

 Alantolactone is the principal constituent of the oil of Inula 

 Helenium. 



NITROGEN AND SULPHUR COMPOUNDS occur frequently in the 

 aqueous distillates of plants yielding volatile oils. Hydrocyanic 

 acid is readily detected by means of Prussian blue, and occurs in 

 the distillates not only of cyanogenetic plants but in a "large num- 

 ber of others as well. The mustard oils 'are esters of isothio- 

 cyanic acid and are characterized by their penetrating odors. 

 Allyl mustard oil is obtained from the seeds of Sinapis nigra and 

 a few other plants of the Cruci ferae. (Consult " The Volatile 

 Oils," Gildemeister and Hoffman, translation by Edward 

 Kremers ; also " Semiannual Reports," by Schimmel & Co.) 



FORMATION OF VOLATILE OILS. The chemical study of 

 odorous principles shows that they vary considerably in their* 

 composition. Not much is known regarding the formation of 

 volatile oils. Charabot and Herbert have suggested that the esters 

 may originate in the cells containing chloroplastids. They suggest 

 that under the influence of an enzyme of reversible activity the 

 esters are formed from the acids and alcohols present in the plant 

 cell, and that they continue to form until the flowering period. 

 They are then diffused to other parts of the plant, notably 

 the inflorescence. While some of the oils are indirect products 

 connected with photosynthesis, others arise through the decom- 

 position of a mother substance, as the glucosides, and still others 

 originate as a metamorphosis of the cell-wall. 



PHYSIOLOGICAL ROLE OF OILS. It is usually considered that 

 volatile oils occurring in receptacles near the surface of the plant, 

 as in fruits like the orange, serve to prevent the entrance of 

 animal and vegetable parasites, and thus prevent disease. Again, 

 the oils which are found in glandular hairs covering the leaves 



