annulus
annulus
1. One of a series of concentric rings or bands of varying width and opacity which are formed in the scales of bony fish. Winter rings are often narrower and denser than summer rings. The number of annuli is indicative of the age of a fish.
2. In the fruit bodies of certain agarics, a remnant of the partial veil that adheres as a ring of tissue around the stipe.
3. A ring of cells around the sporangium of some ferns. The walls of these cells become progressively thicker around the circumference, so inducing tension as they dehydrate, eventually causing the rupture of the sporangium (the point of breaking is called the stomium). The lid of the sporangium then curls back, releasing the tension induced by the annulus in a spring-like motion serving to aid spore dispersal.
1. One of a series of concentric rings or bands of varying width and opacity which are formed in the scales of bony fish. Winter rings are often narrower and denser than summer rings. The number of annuli is indicative of the age of a fish.
2. In the fruit bodies of certain agarics, a remnant of the partial veil that adheres as a ring of tissue around the stipe.
3. A ring of cells around the sporangium of some ferns. The walls of these cells become progressively thicker around the circumference, so inducing tension as they dehydrate, eventually causing the rupture of the sporangium (the point of breaking is called the stomium). The lid of the sporangium then curls back, releasing the tension induced by the annulus in a spring-like motion serving to aid spore dispersal.
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annulus