GEiDWTH AND HARVESTING OF PERFUME PLANTS. 31 



The method of handling must be adapted to the particular plant to 

 be grown. 



A thorough cultivation of the field is necessary to eliminate all 

 weeds, both between the rows and in the rows themselves. This is 

 of the utmost importance, since weeds, although as a rule not con- 

 taining any volatile oil, do possess volatile substances which are set 

 free by the steam should the weeds become mixed with the aromatic 

 plant. A contamination of the oil and a depreciation in the aromatic 

 qualities will result unless the material is kept free from weeds and 



other rank growths. 



HARVEST. 



Possibly no stage in the cultivation and production of volatile oils 

 from plants is of greater importance than that of the proper harvest- 

 ing of the crop. It is usually conceded that most perfume plants 

 reach their maximum development as regards odor, both in quality 

 and quantity, at the flowering period. On the other hand, many 

 authorities are of the opinion that as soon as a plant reaches its full 

 flowering period there sets in a gradual consumption of the odorous 

 principles ; hence, the harvest should be made prior to this consuming 

 process. 



Experiments recently conducted for the purpose of determining the 

 amounts of odorous constituents of several plants present at various 

 stages of development seem to indicate that both the quality and the 

 quantity of the oils vary appreciably during their successive stages 

 of development, but no evidence was obtained to show that consump- 

 tion of odor took place during flowering. However, it was proved 

 that the odor was developed during the advance in growth and the 

 approach of the flowering period. 



Three typical plants were used as a basis of experiment, viz, pepper- 

 mint {Mentha jni^etita)^ bergamot mint {Mentha citrata), and worm- 

 wood {Artemisia absinthium), the oil of each of Which owes its 

 characteristic fragrance to esters which admit of being measured 

 quantitatively with some accuracy. The plants were grown under 

 like conditions and distillations conducted at three well-defined stages 

 of advancement, namely, (1) before flowering (or while in the bud- 

 ding state), (2) at flowering, and (3) after flowering (or during the 

 fruiting stage). 



The effect of successive stages of growth upon the esters and the 

 alcohol only wnll be considered here, although other constituents, and 

 especially the terpenic compounds, also suffer changes. 



195 



