Our first view of marionette-like Claas Claasen and his farm -- with straight, barebranched trees perched precariously near the horizon and a pearlescent moon overhead -- is almost a visual pun on Henri Rousseau's Winter Carnival. But Ms. Schroeder's imagination proves its versatility as little, self-propelled Tractor Max chugs his way through fall and winter until, in a driving spring rain, he becomes mired in mud and has to be rescued by the old farmhorse Florian whom he had proudly spurned. In the end Florian and Max, friends at last, bask in the golden summer wheatfields. At times the principals seem almost overwhelmed by the vast, perspectiveless landscapes and primitivistic details like the rabbits scampering from the tractor's path and the discrete, globular peas resting on Claas' fork. But these illustrations do more than decorate; they define a naive, playful world where a horse can love a tractor without appearing ridiculous.