Louis Sullivan's phrase "form (ever) follows function" became a battle-cry of Modernist architects after the 1930s. The credo was taken to imply that decorative elements, which architects call "ornament," were superfluous in modern buildings. However, Sullivan himself neither thought nor designed along such dogmatic lines during the peak of his career. Indeed, while his buildings could be spare and crisp in their principal masses, he often punctuated their plain surfaces with eruptions of lush Art Nouveau and something like Celtic Revival decorations, usually cast in iron or terra cotta, and ranging from organic forms like vines and ivy, to more geometric designs, and interlace, inspired by his Irish design heritage. Probably the most famous example is the writhing green ironwork that covers the entrance canopies of the Carson Pirie Scott department store on South State Street in Chicago. These ornaments, often executed by the talented younger draftsman in Sullivan's employ, would eventually become Sullivan's trade mark; to students of architecture, they are his instantly-recognizable signature.