Most of the time people use this colloquial terminology for sympodial orchids, because the potential growth can often be seen. "Eyes" are perhaps most easily seen in Cattleyas. Monopodial orchids develop growths from meristems buried under leaf bases that clasp their stems, so the eye is not visible.
Look at the very base of the pseudobulb, where it joins the rhizome. You may need to remove the sheaths. Cattleyas tend to alternate new growths to the left and right from previous pseudobulbs. On the newest growth, in the appropriate spot, you will see a round elevated nub. That is the eye yet to come. The one most likely to develop is usually larger than the others.
If the main eye is damaged, subsidiary eyes may sprout. Many Cattleyas, especially hybrids, will sprout from more than one eye at the same time.
As with most plants, there is a meristem at the base of almost all orchid leaves and sheaths, and under some circumstances these may develop into new growths. This typically happens when all the usual eyes on the rhizome are gone. These meristems may produce flower stem plantlets, in Phalaenopsis, for example, or may flower in future years.
Oncidiums and their hybrids fairly frequently grow a new plant from the apex of a solitary pseudobulb, especially if the rhizome is damaged, or all the eyes have already sprouted.
Active eyes bulge, enlarge and grow. Dormant eyes remain small, but the roundish outline is still visible.
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