This section is from the book "Commercial Gardening Vol2", by John Weathers (the Editor). Also available from Amazon: Commercial Gardening, A Practical & Scientific Treatise For Market Gardeners.
These are obtained from plants that are grown in their pots all the season, by the end of which they have formed plump little tubers and are sold during the autumn and winter. These are the only type that can be used for export purposes, when distance and time are factors, and can be sent to any part of the world. They are also largely used for propagating purposes in this country.