When I am using Cloud texture as bump map in Blender Render, this cells appear. How can I make them go away?
You might consider settings like this.
Influence [Color] and No influence [Normal]
It is not clear that the User can use all clouds as a Normal Map. Normal Map and Bump Map are different.
Any one can paint a bump map manually. That is not true of Normal map. Normal Maps can baked.
You may also want to see the Displacement Modifier which uses textures.
Short answer, rather than a complete technical answer.