Sevcik's Cello School of Bowing Technique, Op. 2 Part 2, by Otakar Sevcik, is part of the Music Sales America series published by Bosworth. This excellent series covers triplets and semiquavers, developing a soft tone, sustained tones, and economizing bow length.
Part 3 of Otakar Sevcik's School of Bowing Technique for Cello, Opus 2, from the Music Sales America series published by Bosworth, features numerous wrist suppleness exercises.