According to Chesnut[13] there are 16,673 leaf-bearing plants included in Heller's Catalogue of North American Plants, and of these nearly five hundred, in one way or another, have been alleged to be poisonous. Some of these are relatively rare or for other reasons are not likely to be eaten by man or beast; others contain a poison only in some particular part, or are poisonous only at certain seasons of the year; in some the poison is not dangerous when taken by the mouth, but only when brought in contact with the skin or injected beneath the skin or into the circulation. There are great differences in individual susceptibility to some of these plant poisons. One familiar plant, the so-called poison-ivy, is not harmful for many people even when handled recklessly; it can be eaten with impunity by most domestic animals.
The actual number of poisonous plants likely to be inadvertently eaten by human beings is not large. Chesnut[14] has enumerated about thirty important poisonous plants occurring in the United States, and some of these are not known to be poisonous except for domestic animals.[15] Many of the cases of reported poisoning in man belong to the class of exceedingly rare accidents and are without much significance in the present discussion. Such are the use of the leaves of the American false hellebore (Veratrum viride) in mistake for those of the marsh-marigold[16], the use of the fruit pulp of the Kentucky coffee tree (Gymnocladus dioica) in mistake for that of the honey-locust[17], the accidental employment of daffodil bulbs for food, and the confusion by children of the young shoots of the broad-leaf laurel (Kalmia latifolia) with the wintergreen.[18] One of the most serious instances of poisoning of this sort is that from the use of the spindle-shaped roots of the deadly water hemlock (Cicuta maculata) allied to the more famous but no more deadly poison hemlock. These underground portions of the plant are sometimes exposed to view by washing out or freezing, and are mistaken by children for horseradish, artichokes, parsnips, and other edible roots. Poisoning with water hemlock undoubtedly occurs more frequently than shown by any record. Eight cases and two deaths from this cause are known to have occurred in one year in the state of New Jersey alone.
Fig. 1.—Conium maculatum. The fresh juice of Conium maculatum was used in the preparation of the famous hemlock potion which was employed by the Greeks in putting their criminals to death. (From Applied and Economic Botany, by courtesy of Professor Kraemer [after Holm].)
An instance of food poisoning to be included under this head is the outbreak in Hamburg and some thirty other German cities in 1911 due to the use of a poisonous vegetable fat in preparing a commercial butter substitute.[19] In the attempt to cheapen as far as possible the preparation of margarin various plant oils have been added by the manufacturers. In the Hamburg outbreak, in which over two hundred cases of illness occurred, poisoning was apparently due to substitution of so-called maratti-oil, derived from a tropical plant (Hydrocarpus). This fat is said to be identical with oil of cardamom, and its toxic character in the amounts used in the margarin was proved by animal experiment. Increasing economic pressure for cheap foods may lead to the recurrence of such accidents unless proper precautions are used in testing out new fats and other untried substances intended for use in the preparation of food substances.[20]
Fig. 2.—Cicuta maculata (water hemlock); A, upper part of stem with leaves and compound umbels; B, base of stem and thick tuberous roots; C, cross-section of stem; D, flower; E, fruit; F, fruit in longitudinal section; G, cross-section of a mericarp. (From Applied and Economic Botany, by courtesy of Professor Kraemer [after Holm].)