178 



SCIENTIFIC AND APPLIED PHARMACOGNOSY 



citric acids, chiefly in the form of salts; calcium oxalate, and ash 

 about 10 per cent. 



The aroma of hops, which is an important factor in judging 

 them, is due to a volatile oil. Several factors influence the com- 

 position of the oil and also the aroma, viz., climate, soil, etc. 



The volatile oil of hops has been shown to consist chiefly of the 

 terpene myrcene, the heptoic, octoic, and nonoic acid esters of the 

 alcohol myrcenol, and the sesquiterpene humulene, with traces of 

 free acids, formaldehyde, and probably some free alcohols. The 

 constituents of chief importance as regards odor are the above-named 

 esters, which constitute a large portion of the oil. 



The several oils examined by Rabak (Journal of Agricultural 

 Research, Vol. II, No. 2) have been found to contain varying pro- 



FIG. 75. Lupulin: a h, successive stages in the development of the glandular 

 hairs on the bracts and floral envelopes of Humulus; g, longitudinal section 

 through a mature hair as seen at h; i, glandular hair with the cuticle raised 

 due to the accumulation and pressure of the oily secretion beneath it. 

 After Holzner. 



portions of the esters, as well as the terpene myrcene and the ses- 

 quiterpene humulene, the variable content of esters being most 

 significant. The curves of the ester content of the various oils and 

 fractions of the oils show at a glance the remarkable differences in 

 the oils from the several geographical sources. The courses fol- 

 lowed by the imported oils are most conspicuous because of their 

 constantly lower ester content. More remarkable is the fact that 

 the ester content of the imported oils remains lower from year to 

 year, practically every sample under observation possessing an 

 exceedingly low ester value. The oils from the California hops are 

 both physically and chemically very similar from season to season. 



