Sentence:  When the smaller facet-planes of Analytical Cubism were placed upon or juxtaposed with the large , dense shapes formed by the affixed materials of the collage , they had to coalesce - become `` synthesized '' - into larger planar shapes themselves simply in order to maintain the integrity of the <WSD>picture</WSD> plane . 
Meaning of the word marked with <WSD> tags:  the plane that is in the foreground of a drawing or painting; coextensive with but different from the objective surface of the work