The authors discuss two aspects related to the radial dependence of spatial density of interplanetary dust. First, they ask which spatial distribution the dust source should have to lead to the observed relative spatial distribution. Sources limited to a shell at several AU heliocentric distance are found to be inadequate, while extended (0.1 AU ≤ a ≤ 10 AU to 20 AU) sources with the semimajor axes distributed ≡a-1.0 or ≡a-1.1 reproduce the observed density gradient. Second, the authors ask whether collisions in interplanetary space would destroy enough of the larger meteoroid particles to create a sufficient supply of dust-sized debris. This is found to be the case. In addition, the extended dust source resulting from these collisions approximately has the spatial distribution required to fit the observed radial dependence of dust density. The authors therefore consider radio and photographic meteoroids as the mass reservoir from which the interplanetary dust cloud is maintained.