Sheep have been observed to be particularly variable in their choice of food plants, not only individually in the flock, but from day to day. Chesnut and Wilcox remark[1] that “there seems to be no way of accounting for the appetite or taste of stock. This statement is perhaps especially true of sheep. We have often observed sheep eating greedily on one day plants which they could scarcely be persuaded to eat on the following day on the same range.” In the case of one flock of sheep on a foothill range at an altitude of 4,600 ft. “a few of the sheep were observed eating large quantities of wild sunflower (_Balsamorhiza sagittata_), a few ate freely of false lupine (_Thermopsis rhombifolia_), some confined their attention largely to the wild geranium, while others ate false esparcet (_Astragalus bisulcatus_) almost exclusively. Two sheep were seen eating the leaves of lupine, and about fifty ate a greater or less quantity of _Zygadenus venenosus_, while the majority of sheep in the band fed exclusively upon the native grasses on the range.” Footnote 1: “The Stock-Poisoning Plants of Montana,” V. K. Chesnut and E. V. Wilcox. _Bul. No. 26. U.S. Dept. Agric., Div. Bot._, 1901. Horses also have been known to acquire in America a depraved appetite for horsetail and loco-weed. The different species of live stock are often quite differently affected by poisonous plants, some being very susceptible to a given plant while others may be little or not at all susceptible. One species (_e.g._ the pig) may readily vomit the poison of a plant which is emetic, while another (_e.g._ the horse) may be unable to do so and hence be the more seriously injured. The variability of the different classes of live stock in this respect is frequently brought out in Chapters II to VI. Poisonous effects may also vary with the individuality and age of animals of the same species. At certain periods of the year—_e.g._ in early spring, and during dry summers,—there may be a scarcity of green herbage, and this may induce animals to eat any green plants which are especially early, including poisonous ones, which they would otherwise refuse. In some cases poisonous plants which do not lose their toxic properties on drying (_e.g._ meadow saffron) may be included in hay, and hence find their way to stock in such a form that they may not be distinguished. It has been found, however, that some poisonous plants or parts of them are refused by stock when mixed with good herbage in hay. Care should be exercised that poisonous plants are not included with hay or green fodder, and in cases of poisoning all forage should be examined.