Seaweed sporangia. Light micrograph of a section through the sporangia layer (purple) of a kelp seaweed, the sea belt (Saccharina latissima). At bottom is the epidermis layer (orange). Reproduction is asexual. Epidermal cells grow into two types (pink filaments): single-celled paraphyzes (top part) and sporangia (bottom part). The spores (round, blue, seen within sporangia) are liberated from here into the sea, where they change in zoospores (that can swim) and settle on rocks to form new seaweed plants. Some released spores are visible at upper right. Magnification: x138 when printed at 10 centimeters wide.