CAUSES OP THE EVOLUTION AND EXTINCTION OP THE TITANOTHERES 



869 



thoroughly dried. Cattle on the range then take the 

 loco and lupine (idem, p. 29). 



Enforced migration and poisonous plants. — Chesnut 

 observes (idem, p. 21) that domesticated animals 

 when feeding quietly on the range exercise considerable 

 choice in selecting forage plants, but that when they 

 are being driven 6 or 8 miles a day they may be forced 

 by hunger to bite off almost all kinds of plants that 

 grow along the course of their travel. Enforced 

 migration among wild animals might similarly cause 

 them to become less fastidious about food. 



Distribution oj poisonous plants. — The chief poison- 

 ous plants of the Montana stock ranges (Chesnut, 

 1901.1) are the death camass (Zygadenus), favored 

 by moderate moisture and taken by sheep; the "tall 

 larkspur" {Delphinium glaucum), favored by moderate 

 moisture, taken by cattle; the "purple larkspur" 

 (D. iicolor), taken by sheep; the water hemlock 

 (Cicuta), found along watercourses, taken by cattle 

 and sheep; the white loco (AragaUus), taken by horses, 

 sheep, and cattle. Lupines (Lupinus) in certain 

 stages of growth are poisonous to sheep. Ergot 

 {Claviceps purpurea) occurs in Montana on a variety 

 of grasses and is occasionally poisonous to horses and 

 cattle, producing a disease of the limbs. On a large 

 ranch of Wyoming, according to Walter Granger 

 (letter, 1904), ergot appeared as a result of irrigation, 

 rendering a large tract fatal to horses and cattle by 

 causing a disease of the hoofs. 



A leguminous plant of Egypt (Lotus arabicus), 

 recently investigated by Dunstan and Henry, as a 

 growing plant is poisonous to horses, sheep, and 

 goats. It contains a glucecoid termed "lotusin," 

 which is poisonous when taken into the stomach 

 (Chesnut, 1902.1, p. 1019). Its seeds when ripe, 

 however, are commonly used as fodder. 



Narcotic plants. — Among narcotic plants "loco 

 weeds" are the most interesting as one of the possible 

 causes of the extinction of wild animals. "Loco," 

 a Spanish word meaning mad or crazy, is applied in 

 northern Mexico and the southern United States to 

 certain plants which so affect the brain of animals as to 

 give them all the symptoms of brain disease. As 

 described in the important paper of Chesnut (1899.1, 

 pp. 403, 404) the weeds called "loco" belong to genera 

 of the pea family. He writes (1902.1, pp. 87-90): 



For many years a disease called loco, affecting cattle, horses, 

 and sheep, has been generally known to the stockmen of the 

 western ranges. This disease has most commonly been attrib- 

 uted to the action of certain plants, more rarely to that of 

 alkali. Several species of plants have been suspected of pro- 

 ducing the loco condition in animals and have been called loco 

 plants or loco weeds and also crazy weeds, from the nature of 

 the disease. Nearly all of the plants which have been considered 

 loco weeds belong to two genera of the pea family. Astragalus 

 and Aragallus. These genera are represented by numerous 

 species on the western stock ranges. * * * From a general 

 description given of the loco disease it is apparent that this 

 condition might very justly be termed a perverted appetite. 



* * * 'pjie horse and the sheep are the animals which are 

 most frequently affected by loco disease. Cattle occasionally 

 acquire the loco habit, but the cases are comparatively rare. 

 In certain parts of Montana the habit became so widespread 

 among horses that the raising of them was abandoned until 

 the locoed animals were disposed of and other horses which 

 had not the loco habit had been imported. * * * During the 

 progress of field work in Montana in 1900 about 650 locoed 

 sheep and 150 locoed horses were seen. 



Mechanically dangerous plants. — Occasional losses 

 of stock occur in Montana from plants acting mechan- 

 ically. For example, the sharp-barbed awns of the 

 porcupine grass (Stipa spartea) and squirrel tad 

 (Hordeum juhatum) when the plants are maturing 

 separate and, enteruig the mouth, throat, eyes, and 

 ears of stock, affect the tissues and give rise to ulcers 

 which cause intense suffering and necessitate killing. 

 (Chesnut, 1902.1, pp. 50-51.) Similarly the corn- 

 stalk disease is sometimes attributed to malnutrition 

 or impaction of the alimentary canal. 



In this connection may be cited an observation 

 recorded by Thisel ton-Dyer (1902.1), which happens 

 to bear upon the life of goats: 



The introduction of the sweetbrier into New South Wales, 

 Australia, in many parts of which it is naturalized, affords a 

 striking illustration of the mode in which the balance of nature 

 may be disturbed in a wholly unforeseen way. * * * The fruit 

 of the sweetbrier {Rosa ruhiginosa) consists of a fleshy receptacle 

 lined with silky hairs, which contains the seedlike carpels. 



* * * The hairy linings of the fruit caused the death of a 

 number of goats by forming hairy calculi, which mechanically 

 occluded the lumen of the bowels. These goats were put on 

 the land with the idea that they would eat down the briers and 

 ultimately eradicate them, but the briers came out best and 

 eradicated the goats. The cattle running on the land are also 

 very fond of the brier berries, and from time to time one will 

 die, and on post-mortem [examination] no pathological changes 

 can be found in any of the organs, nor do the hairy calculi 

 appear in them, although their various stomachs are one mass 

 of the brier seeds. 



INSECTS AND PROTOZOA 



The main features of physical environment, such as 

 moisture and desiccation, heat and cold, can not be 

 considered by themselves or solely in relation to the 

 plant life; they must be studied also in relation to 

 the insect life which they condition. Insect and 

 parasitic life is now known to be one of the greatest 

 factors in the numerical reduction and probably 

 therefore in the extermination of mammals. Greater 

 progress has been made in this study than in any 

 other since Darwin's time, yet Lyell and Darwin both 

 adumbrated the modern discoveries. 



Insects and the food supply. — The periodic devasta- 

 tions of certain insects, especially those caused by 

 locusts as cited by Lyell, in Europe, Arabia, India, 

 and northern Africa, are sufficient to cause the 

 reduction of certain species. As Lyell concludes 

 (1872.1, vol. 2, p. 445): 



The occurrence of such events at certain intervals, in hot 

 countries, like the severe winters and damp summers returning 

 after a series of years in the Temperate Zone, may effect the 



