INTEGUMENTARY STUDIES IN THE POLYCARPICAE

Abstract

SUMMARY The histogenetic development of the integuments of two representatives of the Magnoliaceae, Magnolia stellata and M. virginiana, was studied. The mode of development is the same in these two species. The two integuments have a different form of initiation: The inner integument (i.i.) is wholly of dermal derivation, whereas the primordium of the outer integument (o.i.) is formed as the result of cell divisions in the first subdermal cell layer. There is no apical initial or apical growth in either integument. The initials of the i.i. form rows of cells by repeated periclinal cell divisions, which rows develop independently in mutual juxtaposition to form a ring-shaped wall, the whole structure remaining meristematic. The i.i. is mainly three-layered, the o.i. is (in the younger stages at least) four-layered. The micropyle is formed by both integuments. The i.i. only becomes thicker by “secondary” cell divisions in the micropylar region. After fertilization appreciable changes take place in the o.i., the innermost cell layer forming the sclerotesta and the outer layers the vascularized sarcotesta.