Now just as the acorn may in time become the great oak tree, so this simple basis of geometric design is at the root of the compositions of the great Italian pictures and of thousands of other pictures, even to our own day. Their compositions are based upon a geometric plan. The only difference is that your plan is clearly visible, while theirs is more or less disguised. The reason is that they do not fill their spaces, as you did, with simple lines, but with forms--figures, columns, buildings, draperies, trees, hills, and so on. Consequently, when we speak of the “lines” of their compositions, we often mean rather the direction which the figure, or the object whatever it may be, takes. Thus, a standing figure may take the place of your vertical line; the slightly undulating top of the hills behind it may correspond to your horizontal line; a curving group of angels, floating in the air, may suggest your circle; while your diagonal line may be replaced in the picture by the branches of a tree that spread in a diagonal direction. In other words, what you have done (shall I say?) stiffly with compasses and straight-edge, the artists do freely and loosely. Yet, I repeat it, underneath this seeming freedom, if you search for it, you will find the basis of a geometric design. This I hope to show you in the following chapter. Meanwhile, there is another use for contrast that you should know.