This section is from the book "The Steward's Handbook And Guide To Party Catering", by Jessup Whitehead. Also available from Amazon: Larousse Gastronomique.
A pudding material like corn starch, but has a more delicate flavor of its own. Being a product of the West India islands, the powers owning them have done much to stimulate the trade in arrowroot from commercial motives, and numerous recipes may be found in which arrowroot is an ingredient, but corn starch takes its place most completely, whether for puddings, custards, blanc mange, cakes, crackers, etc., and being cheaper crowds it out of the market. In making puddings, about one-third more of arrowroot is required to a certain measure of liquid than of starch, and the price of arrowroot is much higher. It remains the best material, however, for thickening milk for ice cream, and is much, used as a diet for invalids. The name is in reference to arrowroot being obtained from the root of the manioc, which yields at the same time a poisonous sap into which the native Indians dipped the points of their arrows. This all washes out in water, while the pure arrowroot sinks as sediment and is afterwards dried and powdered.