Task: Question Answering
Input (English): Passage: Unusual for a 13th-century Gothic cathedral, most of the windows are of clear glass.
Looking at the windows running along the nave, John L. Ward observed that the window directly above the suspended crucifix is the only one whose uppermost portion is visible. That window directly faces the viewer, revealing intricately designed stained glass panels that show intertwined red and blue flowers. Because the window is so far back in the pictorial space, where perspective is becoming faint, the proximity of the flowers to the crucifix lends them the appearance of coming "forward in space, as if [they] had suddenly grown from the top of the crucifix in front of it."Ward does not believe this a trick of the eye resulting from loss of perspective towards the high reaches of the panel. Instead he sees it as a subtle reference to the iconography and mythology of the Book of Genesis' Tree of life, which he describes here as "reborn in Christ's death". He does acknowledge the subtlety of the illusion, and the fact that neither of the two well known near copies include the motif. The idea of flowers shown as if sprouting from the top of the cross may have been borrowed from Masaccio's c. 1426 Crucifixion, where flowers are placed on the upper portion of the vertical beam of the cross. Ward concludes than van Eyck took the idea even further by showing the flowers emanating from another source, and sought to depict the actual moment where the tree of life is reborn and "the cross comes to life and sprouts flowers as one watches". 
Question: What is the last name of the person who observed that the window directly above the suspended crucifix is the only one whose uppermost portion is visible?
Output (English): Ward.