DR KEITH WHEELER / SCIENCE PHOTO LIBRARY DR KEITH WHEELER / SCIENCE PHOTO LIBRARY
Seaweed sporangia. Light micrograph of a section through a kelp seaweed, the sea belt (Saccharina latissima). This is a region with sporangia (spore-forming structures). The three layers are: the epidermis (orange), the cortex (white and pink), and the medulla (across centre). Reproduction is asexual. Epidermal cells grow into two types (purple filaments): single-celled paraphyses (upper part) and sporangia (lower part). The spores are liberated from here into the sea, where they change in zoospores (that can swim) and settle on rocks to form new seaweed plants. Magnification: x37 when printed at 10 centimetres wide.
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