With ageing, the pseudobulb sheds its leaves and becomes dormant.
From the en.wikipedia.org
The pseudobulb has a smooth surface with lengthwise grooves, and can have different shapes, often conical or oblong.
From the en.wikipedia.org
A pseudobulb then takes over, exploiting the last reserves accumulated in the backbulb, which eventually dies off, too.
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A pseudobulb typically lives for about five years.
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More examples
A solid bulblike enlargement of the stem of some orchids
The pseudobulb is a storage organ derived from the part of a stem between two leaf nodes.
A swollen bulb like part of most orchids that holds the leaves and is attached to the rhizome
Enlarged, bulbous stem segments that often occur on the stems of epiphytic orchids. The plant uses this to temporarily store water and food during times of drought.
A thickened portion of the stem of many orchids functioning as a water and food storage device.
A swollen stem common in several types of orchids that is used by the plant to store moisture and nutrients.
(SOO-doh-buhlb) -- A false bulb, the above ground thickened portion of the lateral branch of sympodial orchids.
The thickened, bulb-like structures of sympodial orchids that consist of several nodes.
Thickened stem near surface, resembling a bulb (seen in orchids).