well known to be chiefly salicylate of methyl, readily prepared from salicylic acid and wood-alcohol; and the oil or essence of pineapple is precisely butyric ether, manufactured largely from waste materials. Acetate of amyl and valerate of amyl are supposed to represent the flavor of the apple and the pear, but how accurately they coincide with the actual flavor-substances of these fruits has not been demonstrated. Formate of ethyl, another compound ether, is used in so-called peach-essence. Numerous fruit-flavors, used for culinary extracts and largely for soda-fountain sirups, are manufactured as mixtures of ethers, by recipes varying with different manufacturers. Many of these, resting on no due authority, are unwholesome mixtures, often spurious imitations of the true fruit-flavors, and again hurtful by reason of excessive proportions. As to the chemistry of the production of flavoring ethers in plants, some guesses were presented under the head of sugar fermentation.
5. Alkaloids.—Substances strongly affecting the nervous system, as medicines or poisons, of course do not occur in the edible fruits, and we are not in the habit of placing potent compounds among the constituents of fruits as a class; nevertheless, when we think of it, no small proportion of the banes and antidotes of the vegetable kingdom is matured in seeds and their coverings. In the poppy-fruit, the capsule or pericarp furnishes at least sixteen distinct alkaloids, including morphine, while the seeds are harmless, and yield an oil much used for food. In the fruit of the nux-vomica, the seeds are deadly with strychnine and other poisonous alkaloids, while the juicy pulp is but very slightly impregnated with these bitter poisons (Fluckiger and Hanbury, "Pharmacographia," p. 384). The seeds of henbane, and stramonium, and the Calabar-bean, contain potent alkaloids. The unripe tomato often contains traces of solanine, a poisonous alkaloid, which disappears during ripening, probably by a glucosic fermentation. The same alkaloid is sometimes found in the green or exposed parts of potato-tubers.
Many of the vegetable alkaloids are stable compounds, having clearly-marked chemical characteristics. Some of the opium-alkaloids closely resemble others in their composition. Different species of the same family often yield the same alkaloids. The theobromine of the chocolate-nut can be changed by the chemist into caffeine, the alkaloid of the coffee-berry. Such an insight has been obtained of the structure of conine, the alkaloid of the classic poison hemlock, that it has been formed from inorganic materials, through the processes of the laboratory. But no evidence has been obtained as to the steps through which alkaloids are formed in the living plants.
It is little enough we know of the productive chemistry of plants. As, at the beginning, we had need to plead ignorance of plant-constituents, still more, at the end of our brief survey, must we declare ignorance of the chemical genesis of those constituents. We can