494 Trans. Acad. Sci. of St. Louis. 



is every indication that, starting about some small nucleus of 

 vegetable fiber, they have been compacted into the dense, 

 felty texture by the visceral movements of the animal, to 

 which, causing friction against one another, their perfectly 

 round form is attributable. 



It is well known that the Opuntias produce spines and two 

 kinds of trichomes. In some of the Cylindropuntias, each 

 spine is invested by a deciduous sheath, which is downwardly 

 barbed, so that a person or animal brushing carelessly against 

 a plant is certain to remove some of the barbed sheaths. In 

 the Platopuntias, to which the ordinary flat-stemmed prickly 

 pears, and the species upon which the Mexican cattle are fed, 

 belong, the spines, when present, are destitute of such a 

 sheath, and protect the plant simply because of their rigidity 

 and pungency. The spines originate in what have been called 

 pulvini, which in this genus of cacti are coated with delicate, 

 flexible hairs, divided by partitions into a number of cells, 

 and stiff, thick-walled hairs, several millimeters in length and 

 from one to two tenths of a millimeter in diameter at the 

 base. These are very lightly attached to the epidermis of 

 the plant, so that when the pulvinus is touched they are cer- 

 tain to be removed in considerable numbers, the fine points 

 of the stiffer ones penetrating the skin, and the barbs with 

 which they are closely beset preventing their ready with- 

 drawal. 



Balls formed largely of the hair of animals are often found 

 in the stomachs of ruminants, to which they have found their 

 way when the animals have licked themselves, and not infre- 

 quently smaller balls, with a hard, glossy surface, are found 

 in the stomachs of cattle, horses and, as Dr. Eschauzier in- 

 forms me, of goats. In general, such a formation is spoken 

 of as a bezoar, and all of the principal agricultural museums 

 contain good s})ecimens of them. One of the largest of the 

 ordinary hair balls which has come to my notice is preserved in 

 the museum of the Iowa Agricultural College, and is stated to 

 weigh four pounds and eleven ounces and to measure twenty- 

 five and one-half inches in circumference. The smaller, 

 harder structures, which seem to be primarily of biliary com- 

 position about some sort of nucleus, rarely measure more 



