UPDATE: answers posted at the end.
Which of these plant specimens doesn't belong? (Images will be properly credited in a forthcoming article which will explain why they're so interesting.)
The images are all the same magnification, but have been colorized so that the color won't give you any clues. Focus on the structure of each specimen, and pick one that doesn't belong with the others. (Insert Sesame Street reference here.)
ANSWER: Picture number 1 is wheat. The rest are Zea mays. See next post.