Minecraft wiki entry for Metadata_variants, associated text: Melon and pumpkin stems also have eight distinct stages of growth. However, instead of having eight individual textures for each of the eight growth stages, each stage reveals two more pixels of the stem texture from the top down, and the tint applied to the stem texture also changes. As a result, since the stems have eight unused upper values in addition to the eight lower used states, the upper states start pulling from the texture below the stem texture on the texture atlas currently in use, and they use extreme tints that cannot normally be applied in normal gameplay. Their wireframe hitboxes would also appear to extend above the bounds of the block when targeted, but attempting to target anything above the height of the block would result in the stem not actually being targeted.