[Chap. XIX 



SUBSTANCES MADE FROM FOOD 



173 



tuie of resins, gums and foods. It is the source of commercial rubber 



(Fig. 64). 



Fig. 64. Interior view of a forest on a rubber plantation in the East Indies. The 

 trees have been tapped to collect the latex from which rubber is made. Photo from 

 Field Museum of Natmal History. 



Essential oils. The odors of flowers, and the odors and flavors of fruits 

 and vegetables are due in part to minute quantities of essential oils. 

 They are often associated with resins and gums and are very unlike the 

 liquid fats ( fatty oils ) . They are of no importance as food, but are highlv 

 prized as flavors and perfumes, and for a few medicinal and industrial 

 uses. You are probably familiar with menthol, camphor, turpentine, the 

 characteristic oils of mint, pine, juniper, wintergreen, geranium, lemon, 

 orange, ginger, anise, cloves, sage, hops, wormwood, lavender, berga- 

 mot, bitter almonds, and vanilla. Some of the essential oils contain 

 sulfur. These underlie the odor and flavor of onion, garlic, watercress, 

 radishes, and many kinds of mustard. 



The edible parts of many plants, such as sweet corn, turnips, peas, and 

 others, when first harvested have a delicious flavor that is lost very 

 rapidly. Some of this loss in flavor is due to the disappearance of essen- 

 tial oils, but a part of it is the result of the oxidation of sugar and of 



