The sporangiophores form a tight layer at the open surface of the pustule under the epidermis of the host. Eventually weathering, and internal pressure caused by growth of the pustule, causes the epidermis of the host to break open and expose the fertile layer. Each sporangiophore blips off a linear series of spherical, hyaline, sporangia to form a white powdery pustules. This is the aesxual reproductive stage whose purpose is to spread the disease throughout the season whewn opportunity permits.