The distribution of heavy elements in the plane and the disk of our own Galaxy is examined from new UBV, DDO, and CMT₁T₂ photometric data of red giants belonging to fifiy open clusters. The metal content is derived from the following four abundances parameters: δ(U-B), δCN, Δ(C-M), and Δ(M-T₁), which take information not only from the blue-ultraviolet spectral region but also from the near red. It is found that: (1) In general, the δ(U-B) and δCN parameters give results very close to those of the Fe+CNO-sensitive Δ(C-M) index of the Washington system. (2) CNO is enhanced with respect to the iron-peak elements in the giant branches of some clusters. (3) Regardless the morphology, age and position in the Galaxy, all the red evolved stars in the same cluster are, in general, identical in chemical composition. This result holds for the clusters having enhancement of the CNO elements. Arguments are presented which allow us to reject the convection as a mixing mechanism of heavy elements to the surface of the stars from interiors. Although no evidence for a variation of [Fe/H] with age in the last 6x10⁸ years is found, this stellar population appears to be, in the mea, neighborhood K giants. These clusters may probably have formed from material which was not sufficiently well mixed during the last ∼6x10⁸ years. On the other hand, although the disk clusters show a clear variation of abundance with age, the metallicity of the younger disk clusters is similar, in the mean, to those of the galactic plane. The existence of an abundance gradient in the disk and the plane of our own galaxy is clearly demonstrated