The Siouan stock is defined by linguistic characters. The several tribes and larger and smaller groups speak dialects so closely related as to imply occasional or habitual association, and hence to indicate community in interests and affinity in development; and while the arts (reflecting as they did the varying environment of a wide territorial range) were diversified, the similarity in language was, as is usual, accompanied by similarity in institutions and beliefs. Nearly all of the known dialects are eminently vocalic, and the tongues of the plains, which have been most extensively studied, are notably melodious; thus the leading languages of the group display moderately high phonetic development. In grammatic structure the better-known dialects are not so well developed; the structure is complex, chiefly through the large use of inflection, though agglutination sometimes occurs. In some cases the germ of organization is found in fairly definite juxtaposition or placement. The vocabulary is moderately rich, and of course represents the daily needs of a primitive people, their surroundings, their avocations, and their thoughts, while expressing little of the richer ideation of cultured cosmopolites. On the whole, the speech of the Siouan stock may be said to have been fairly developed, and may, with the Algonquian, Iroquoian, and Shoshonean, be regarded as typical for the portion of North America lying north of Mexico. Fortunately it has been extensively studied by Riggs, Hale, Dorsey, and several others, including distinguished representatives of some of the tribes, and is thus accessible to students. The high phonetic development of the Siouan tongues reflects the needs and records the history of the hunter and warrior tribes, whose phonetic symbols were necessarily so differentiated as to be intelligible in whisper, oratory, and war cry, as well as in ordinary converse, while the complex structure is in harmony with the elaborate social organization and ritual of the Siouan people. Many of the Siouan Indians were adepts in the sign language; indeed, this mode of conveying intelligence attained perhaps its highest development among some of the tribes of this stock, who, with other plains Indians, developed pantomime and gesture into a surprisingly perfect art of expression adapted to the needs of huntsmen and warriors.