DR KEITH WHEELER / SCIENCE PHOTO LIBRARY DR KEITH WHEELER / SCIENCE PHOTO LIBRARY
Abnormal thistle stem. Light micrograph of a normal (top) and abnormal (bottom) stem of the perennial sow thistle (Sonchus arvensis). The abnormal stem has grown in a flattened, or fasciated, manner. This is thought to be due to injury or infection to the stem meristem (the actively growing tissue), which causes a row of proto-stems to form and then fuse together to form the flattened structure seen here.
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