A histogenetic study of integument development in two juglandaceous genera indicates that in these taxa the integument is formed by both dermal and subdermal cells of the second and third layers of the floral apex (in contradistinction to the exclusively dermal origin recorded in a number of cases). The integument initiates as two individual primordia which coalesce postgenitally to form a circular rim. Subsequently submarginal and subapical initials are formed. After a discussion of the theoretical aspects, the conclusion is drawn that the most plausible explanation of the advent of the inner integument seems to be the so -called syntelome hypothesis.