The interaction of solar radiation with the vegetation is treated in this work. A mathematical approach is used to describe the primary and complementary solar radiation profiles within the space occupiend by the vegetal elements. The generalized solutions for the differential or ìntegro-differential equations defining each term (primary or complementary) are developed. These analytical solutions depend on the optical characteristics of the individual vegetal surfaces and on the function giving the inclination distribution of the elemental vegetal surfaces.