How much success have you had rooting old rootless Cattleya back-bulbs.

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Old Cattleya rhizomes may produce new roots. Some Catts normally produce new roots from the new rhizome just formed on new growth; others normally produce new roots from the older rhizome just before the new growth. When back bulb divisions are potted up, many Catts make new roots from the old rhizome as the new eye breaks.

If successful in the glass of water, I have observed new roots form on the rhizome before the eye breaks.