Clouds may form in clear air. They may also form or grow from other clouds, called “mother clouds”. Depending on the change, one of the following two suffixes may be used:
(a) “Genitus”: A part of a cloud may develop, and more or less pronounced extensions may form. These extensions, whether attached to the mother-cloud or not, may become clouds of a genus that is different from that of the mother-cloud. They are then given the name of the appropriate genus, followed by the name of the genus of the mother-cloud with the addition of the suffix ”genitus“ (for example, Cirrus altocumulogenitus or Stratocumulus cumulogenitus).
(b) “Mutatus”: The whole or a large part of a cloud may undergo complete internal transformation, changing from one genus into another. The new cloud is given the name of the appropriate genus, followed by the name of the genus of the mother-cloud with the addition of the suffix ”mutatus" (for example, Cirrus cirrostratomutatus or Stratus stratocumulomutatus). The internal transformation should not be confused with changes in appearance resulting from the relative movement of clouds and the observer.