It is likely that the painting's masterful design is Leonardo's own, even if the actual execution of most of the panel is not. The composition is divided into two unequal parts. A narrow area on the right is reserved exclusively for the Virgin, whose figure emerges strongly against the vigorous framing provided by the quoins at the corners of the building. On the left, the angel and landscape fill an extended oblong area. However, although the two parts are diversely conceived, they are harmonized and made continuous. This is party achieved by the connecting figure of angel; it estabhlishes a flow of action from the left side to the right as it moves toward the Virgin, who in turn responds to the angel's prophetic gesture. The pictorial unification is also achieved by the repetition of four pine trees arranged at approximately equal intervals across the painting; their verticality is echoed by that of the quoins ascending along the corner of the building. The long, low parapet behind the angel - interrupted just long enough to frame and emphasize the head, hand, and lilies - parallels and underscores the procession of trees and also finds its echo in the horizontal placement of each alternate quoin. Thus, the forms of nature are made to interact with architectural forms and with the figures they enclose.