Bladder wrack, light micrograph. Transverse section through a strand of bladder wrack (Fucus vesiculosa). The male conceptacles (round) contain reproductive parts called antheridia. These liberate spermatozoids (male reproductive cells), which pass through the hole (ostiole) in the top of each conceptacle (some holes seen here). The spermatozoids that successfully enter the oogonia of a bladder wrack with female conceptacles, will then fertilise its eggs. Magnification: x11 when printed at 10 centimetres across.
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