  A model of growth of icosahedral viral capsids is proposed. It takes into
account the diversity of hexamers' compositions, leading to definite capsid
size. We show that the observed yield of capsid production implies a very high
level of self-organization of elementary building blocks. The exact number of
different protein dimers composing hexamers is related to the size of a given
capsid, labeled by its T-number. Simple rules determining these numbers for
each value of T are deduced and certain consequences are discussed.
