146 FLAVORING AND BEVERAGE PLANTS 
(0.06%) very similar to that of mustard if not identical with 
it. This oil is so powerful an irritant that it will raise blisters 
when applied to the skin. Capers are flower-buds of the 
caper-bush (Fig. 145), preserved in vinegar. They contain 
a peculiar acid, and a volatile oil similar to that found in 
garlic. 
Under the head of miscellaneous condiments might also 
be included such sharp tasting vegetables as radish and 
onion which have already been considered. 
Fig. 145, I1].—Caper-bush. Floral diagram. Pod. Seed, entire. Same, 
cut vertically. (Baillon.) 
56. Essences are flavoring substances extracted from 
plants in various ways, often dissolved in water or alcohol, 
and always in liquid form. Peppermint obtained from the 
whole plant (Fig. 146), wintergreen from the leaves and fruit 
(Fig. 147), vanilla from the pods (Fig. 148 I), lemon from 
the rind of the fruit (Fig. 106), and rose from the petals 
(Fig. 148 II, 148 III) are familiar examples. 
In peppermint, wintergreen, lemon, and rose the flavoring 
substance is a volatile oil. In vanilla it is a peculiar crystal- 
line substance called vanillin, which curiously enough occurs 
