Spirogyra – phytoplankton diatoms – brown seaweed ovary, c. s. – Posidonia leaf, c. s. – peacock feather, c. s. – laminar thallus c. s. – corallina officinalis – halopteris scoparia – nostoc – ulva, c. s. – codiaeum variegatum, cross. section. – rhizome of seaweed.