Appendix. 6y 



The production of resins from terpene and cymene oils, now 

 that these are seen to be aromatic hydrocarbons, explains the 

 ease with which other aromatic bodies (benzene, toluene, phenol, 

 etc.) are obtained from resins, — for it can now be more than sur- 

 mised that in this round of changes the benzene ring is never 

 broken. 



In the summary of Wittstein, of the 114 natural orders, 28 

 are reported to contain resins; of these 28 orders, 16 contain 

 essential oils with the resins and 1 2 do not. On the other hand, 

 there are 45 orders containing volatile oils, 29 of them not being 

 reported as containing resins. Of the 26 orders given as furnish- 

 ing aromatic bodies other than resins and oils, one-half have 

 resins. 



To enter fully into an inquiry as to the chemical history of 

 the aromatic bodies in plants would be to overstep the limits of 

 this paper. Indeed, it may be thought that such an inquiry 

 would overstep the present limits of science. Let us consider 

 what preparation we have and what foundation we have for enter- 

 ing upon such an inquiry. 



In the first place, we have some measure of acquaintance 

 with the structure (or to be more modest, the chemical charac- 

 ter) of aromatic compounds. We know something as to what a 

 given aromatic substance can be formed from, and what can be 

 formed from it, and the conditions needed in both cases. This 

 knowledge is demonstrated by the large number of syntheses 

 which chemical science has effected in the aromatic group. But 

 we must be cautious about assuming that substances producible 

 in the laboratory in a certain way must needs be formed in the 

 plant in the same way. We must recollect that we have already 

 often observed that a given chemical production may be effected 

 in different ways. There are, well known, at least three differ- 

 ent ways of bringing gallic acid out of gallotannic acid : fer- 

 mentation by the natural ferment, "fermentation" by boiling, 

 and oxidation. Bruise a bitter almond kernel with water, and 

 by reason of the emulsin present, bitter almond oil and prussic 

 acid arise in vapor and the solut'^^n becomes sweet with glucose. 



