A down pressure adjustment mechanism for a planter provides a self-contained spring cartridge holding a preloaded compression spring that may be moved between a limited number of mounting points to provide for convenient and significant changes in down pressure without the need for specialized tools or the like. Each cell communicates with at least one other cell of the array, permitting an exchange of data packets between the cells of the array and an exchange of control information between the cells of the array. Also described is a novel HTTP tunneling protocol that may be used by the HTTP tunnel connection layer. As for propeller rotors the number of round bent tubular trapezoids gets multiplied as well as its wind contact surfaces, which results in the optimum use of most centrifugal propelling forces thanks to the reduction of wind entrance and the amplification of wind exit. The second recess extends from a second side of the main body portion to the middle section. Stable zeolitecellulose composite material characterized in that leaching of the zeolite phase does not occur upon contact of the composite with water at approximately 373 K comprises a zeolite and a stable cellulosic fiber prepared as described above, the composite material being formed by contacting a zeolite with the stable fiber material.